The Eurypterida of New York/Volume 1/Eurypteridae
VIII
SYSTEMATIC ACCOUNT OF THE EURYPTERIDA
Class arachnida
Subclass merostomata (Dana) Woodward
Order eurypterida Burmeister
Family eurypteridae Burmeister
Genus strabops Beecher 1901
Strabops thacheri Beecher
Strabops thacheri Beecher. American Journal of Science, n. s. 12:365, 1901
An eurypterid of extraordinary interest because of its age and completeness is a specimen obtained in the Cambric Potosi limestone of St François county, Missouri, which was studied by Prof. C. E. Beecher, and made by him the type of the genus and species: Strabops thacheri. Professor Beecher, evidently without his own knowledge had the use only of the relievo of this specimen and the counterpart has bsen found by the authors in the collections of Columbia University. The specimen is so preserved that the interior view of the dorsal side is shown in both cast and mold, and the latter is obviously the more distinct. Had it been at the disposal of the describer it would probably have prevented some evident misconceptions of structural details. The intaglio, cleaned with potash [pl. 4, fig. 5] and sharply cast [pl. 13, fig. 2], exhibits quite distinctly all true structure lines.
The specimen was correctly recognized by Dr Beecher as suggesting the genus Eurypterus. Its differences from the latter genus which, as such, constitute the generic characters were set forth by him as follows:
The cephalothorax is comparatively shorter and wider than in Eurypterus, the eyes are further forward, nearer together, and more oblique, and besides the telson but 11 abdominal somites can be determined on the dorsal side, instead of 12, as in Eurypterus. These differences are considered as indicative of a new genus and it is proposed to recognize this type under the name Strabops nov. gen., with Strabops thacheri n. sp. as the type species. The generic name is in allusion to the inward turning or squinting of the eyes.
Two of the differential characters here cited, viz, the anterior position of the eyes and the absence of one somite, are not verified by the counterpart. 
Figure 31 Strabops thacheri Beecher. Outline of original drawing The supposed eyes, which were represented as oblique ovate cavities with the visual surfaces apparently broken out [see original figure, copied here in text fig. 31], are small lumps of the underlying rock held in place by the overlapping fold which has formed near the frontal margin by a shoving of the specimen. These have been chiseled out on the counterpart and the surface of the folded part of the carapace exposed. The real eyes are seen in our specimen half way between the anterior and posterior edges, near the lateral margin. They are small and circular.
The other difference concerns the number of abdominal somites on the dorsal side, for the intaglio and the plaster cast therefrom seem to leave no doubt that Strabops agreed with the later eurypterids in having 12 segments. The 1st segment is for the greater part pushed under the carapace, and the next, the 1st in Beecher's figure, is shown only on the right side of the bent specimen; on the other side the bending of the abdomen has forced it back over the 3d tergite.
With these corrections of structure, Strabops stands still closer to the Siluric Eurypterus than it appeared to Beecher; in fact it is obvious that all the principal parts of eurypterid structure are already fully fixed in this Cambric progenitor; the carapace, preabdomen, postabdomen and telson exhibiting the same general characters and number of component parts. Notwithstanding this conformity in structure Strabops presents a number of distinctly primitive characters which indicate its closeness to the archetype of the eurypterids. We see the most important of these in the lack of differentiation in width and length between the preabdominal and postabdominal segments, the contraction of the postabdomen taking place so uniformly that the conventional division between body and tail, so evident in all later eurypterids, is here still entirely undeveloped. The postabdomen, always a slender part of the body with much lengthened posterior segments in later forms, is here short and broad, the segments not at all increasing in length backward. Altogether, all abdominal segments retain a highly primitive and simple aspect in their appearance as uniformly narrow straight bands that hardly bend forward at the lateral extremities. The first tergite, however, has progressed in development beyond the others, and, as in the Siluric genera, is more closely connected with the carapace than with the abdomen, and is distinctly bent forward at the extremities.
The carapace is distinguished from that of the Siluric descendants by its remarkable shortness, or relatively very small size which may also constitute a primitive feature.[1] On the other hand the doublure or rim of the underside is very broad, suggesting the genus Stylonurus. The eyes are especially notable for their small size and circular outline.
The telson spine is short and plump, and thus in correspondence to the short compact body.
Of the limbs but a single fragment is shown, and this is too small to indicate their character. Doubtless they correspond in lack of differentiation with the dorsal test and were probably all of simple and similar form, slightly increasing in length posteriorly. Strabops has served in our effort to reconstruct the archetype of the Eurypterida.
To sum up the foregoing distinctive features in Strabops, we find that the lack of differentiation of the parts of the abdomen and the general primitive aspect of the form, together with the high geologic age of the genus warrant its recognition as distinct from Eurypterus, though it is manifest that the form is very similar thereto.
Genus EURYPTERUS DeKay 1825
The genus Eurypterus embraces not only those representatives of the order Eurypterida longest known and most completely understood, but it also surpasses all other genera in the number of species and in geological and geographical range; it represents the most vigorous and the most typical genus of the order, although it does not contain the giants of the group. It is therefore very proper that it should have given its name to this remarkable order of the class Arachnida.
The genus was erected by James E. DeKay in 1825 for the most common of the New York species, viz, Eurypterus remipes. The organization of the body of Eurypterus was first elucidated and elaborately described by Nieszkowski [1858] and James Hall [1859]; the former basing his observations on the finely preserved material from the island of Oesel in the bay of Riga, Russia, the other on that from the waterlimes of New York. Hall described seven supposed species from the New York rocks, viz, E. remipes, microphthalmus, lacustris, robustus, pachychirus, dekayi, pustulosus, to which a few have been added since from the rocks of this State, viz, E. (?) prominens Hall and Clarke [1888], E. pittsfordensis Sarle [1902] and E. maria Clarke [1907]. A form from the Guelph dolomite of Canada (E. boylei Whiteaves), two from the waterlime of the same horizon at Kokomo, Indiana (E. kokomoensis Miller & Gurley and E. ranilarva nov.) a small number of species from the Carbonic of Illinois and Pennsylvania (E. mazonensis, E. mansfieldi, E. pennsylvanicus, E. potens, E. stylus and E. approximatus); and the species E.? megalops, E. pristinus and E.? (Dolichopterus) stellatus from the Frankfort shales complete the list of North American representatives of the genus.[2]
In Europe a considerable number of species were described by Salter and Woodward but the principal advance in the knowledge of the genus and its structural details has been made by F. Schmidt [1883] and Holm [1898]. Both of these authors described the E. fischeri from Oesel, which had already served as the subject of Nieszkowski's investigations and was at that time identified with E. remipes DeKay. Schmidt corrected and supplemented in many ways Hall's and Nieszkowski's descriptions of the endognathites, demonstrated the presence of five separate sternites (Hall knew but one, the operculum, and Nieszkowski assumed six) and showed that they are open on the ventral side. He further pointed out differences in the appendages of the first and second sternites in individuals otherwise alike and attributed these to sexual differences. In the dolomite marls of Oesel these merostomes are not preserved as in the waterlimes of New York where the integument is fully carbonized. By most skilful manipulation Holm succeeded in removing from the matrix the integumetal film of E. fischeri and was thus enabled to study these parts by transmitted light, and to describe the structure of the integument with a completeness that could be equaled only from the living organisms themselves. We shall not here enter upon a detailed review of the results of his investigations, but shall point out the more important of the determinations, since there is no reason to doubt that entirely similar structures existed in the closely related species E. remipes and E. lacustris. Indeed, our material verifies several of his detailed discoveries referred to below.
The absence of facets in the compound eyes was conclusively shown by transmitted light. On the underside of the cephalothorax the presence of preoral chelicerae in place of antennae, already inferred by Schmidt, was demonstrated,[3] [see restoration pl. 3, fig. 1]. The fifth segment of the second endognathite in the male carries a long, curved, tubular process [text fig. 32] which, by analogy with Limulus, Holm considered as a clasping organ employed during copulation. The epicoxite of the coxal segments before observed by Laurie in Slimonia and Pterygotus, was found in its proper position in Eurypterus and a circular perforation with very thin covering membrane has been observed close to the inner margin of the coxa of the fourth endognathite [see text fig. 12; pl. 7, fig. 6]. 
Figure 32 Second endognathite of E. fischeri with clasping organ of male; the long reflexed hornlike appendage of underside. (From Holm) A corresponding organ in the living Limulus polyphemus was discovered by Holm on the coxae of the third and fourth endognathites near the epicoxite. On account of the structure of this organ and its position on that side of the coxa which is turned toward the outside, it was suggested that it has an auditory function. This structure has also been observed by Sarle in Hughmilleria socialis [pl. 62, fig. 5] and by the writers in E. remipes [pl. 7, fig. 6]. A new organ was discovered, the endostoma. This consists of a small, thin, deeply emarginate shield, not clearly bounded on the sides, which formed the inner posterior margin of the mouth [text fig. 13].[4] Further, the connection of the metastoma with the ventral integument of the cephalothorax by a doublure [text fig. 14] was shown. The distinction between male and female genital appendages was clearly elaborated and the presence demonstrated of an interior paired, curved, tubular organ connected with the female genital appendage [text fig. 19]. A like pair of tubes has been found by the writers in E. remipes and lacustris [pl. 12, fig. 2]. Finally, the delicate membranes of the interior of the ventral side and the oval attachment areas of the gill plates were described and reproduced by photographs.
It so happens that E. fischeri, which thus has become known down to the least details of its integumental structure, differs very little from the genotype of Eurypterus, E. remipes; and both Schmidt and Holm have suggested that these with E. lacustris may be only geographical varieties of the same species, inasmuch as they appear at the same geological horizon. But the question remains open whether E. remipes, the genotype by right of priority, is a faithful expression of the structure displayed by the genus Eurypterus. To determine this point we may briefly survey the phylogenetic relations of the species of Eurypterus.
The American species of Eurypterus readily fall into three subdivisions, viz, (a) those that group themselves around E. remipes; (b) those that vary in different directions from this group but are approximately contemporary; and (c) the later Carbonic species. Group (a) is represented by E. remipes, E. lacustris and its var. pachychirus, E. pittsfordensis, and possibly also E. maria. It is Eurypterus sensu stricto. Group (b) is a diffuse association comprising aberrant species E. dekayi, E. microphthalmus, E. pustulosus, E. kokomoensis, E. prominens and E. boylei. Eurypterus microphthalmus is representative of a small group, also present in England (E. brewsteri), characterized by its small compound eyes and broad, short cephalothorax. Eurypterus dekayi is probably a branch from E. lacustris with a number of characters already suggestive of approach to a phylogerontic condition. Eurypterus pustulosus, although attaining immense size, is aberrant in the exaggerated development of the tuberculation. Eurypterus kokomoensis stands apart in a number of characters, especially in the clawlike development of the ninth or terminal segment of the swimming leg, and it is made the type of the subgenus Onychopterus. Eurypterus prominens has a long carapace with eyes well forward, characters that are also present in the young of E. remipes. Eurypterus boylei, from the Guelph formation, also exhibits proof of aberrant development in the large median tubercles of the tergites. Group (c) shows distinct phylogerontic characters in the strong development of the spines, surface scales and other excrescences, as well as in the large epimeral pieces of the postabdominal segments, and these are comprised under the subgeneric term Anthraconectes.
The group Eurypterus sensu stricto, or as represented by division (a), embraces not only the relatively simplest expression of the genus around which the other forms quite naturally group themselves, but also the most vigorous and that which dominates the stage (Salina) where the genus clearly reaches its climacteric development. The Eurypteri of the Bertie waterlime, notably E. remipes and E. lacustris, are therefore properly considered as representing the typical expression of the genus.
The genus thus defined is characterized by an elongate, slender body, widest in the middle of the preabdomen and distinctly differentiated into preabdominal and postabdominal regions. The carapace is subquadrate to subrectangular in outline, with rounded anterior angles, relatively small, one fifth to one seventh the total length of the body. The compound eyes are reniform, without distinct facets; situated on the dorsal side of carapace. The ocelli are situated between the compound eyes. The chelicerae are small, not extended beyond the edge of the carapace. The endognathites increase in length from the first backward; the first three pairs relatively robust, short and spinous; the fourth pair slender and bearing only a terminal spine with two spines on the penultimate segment. The fifth pair is developed into swimming legs with bladelike and extended seventh and eighth segments. Its ninth segment is rudimentary. The ventral membrane of the cephalothorax is separated by a distinct suture from the doublure of the carapace, but no epistoma is formed. The metastoma is oval in outline, but slightly emarginate in front. The tergites and sternites are more or less bandlike and plain as in other genera; the male opercular appendage is small, with simple median lobe; that of the female long, extending to the third sternite and beyond, consisting of two paired and two single members, the paired members forming two pentagonal basal pieces, and two clawlike terminal pieces. The single imbricating lobes form the long median part. They are produced into lateral points at their posterior extremities. Two curved, interior tubes are connected with the female organ. The postabdominal segments are bandlike rings. The telson is long, spinelike, flat on the dorsal side and carinate on the ventral side.
Several species which have currently been brought under Eurypterus are here shown to belong to Eusarcus and to differ in a number of characters of generic value, viz, the form of the carapace which is triangular, the marginal position of the compound eyes, the decrease backward of the endognathites and the spinosity of all legs, the form of the metastoma, which is subtriangular and the broad and flat preabdomen. The differences of Eurypterus from the other genera are well known and for the most part manifest. They consist principally in the position of the lateral eyes, the absence of distinct facets, the different development of the chelicerae and endognathites, the form of the metastoma, of the opercular appendages and of the telson.
The North American species are given in the following list, those found in New York being distinguished by an asterisk. The list is in ascending order.
| Lower Siluric | Upper Siluric |
| FRANKFORT SHALE | CLINTON BEDS |
| *E. megalops nov. | *E. prominens Hall |
| *E. pristinus nov. | KOKOMO WATERLIME—(=Lockport) |
| *E. ?(Dolichopterus?) stellatus nov. | E. kokomoensis Miller & Gurley |
| E. ranilarva nov. |
| Upper Siluric | |
| GUELPH DOLOMITE | *E. pustulosus Hall |
| E. (Tylopterus) boylei Whiteaves | MANLIUS LIMESTONE |
| PITTSFORD SHALE | *E. microphthalmus Hall |
| *E. pittsfordensis Sarle | Carbonic |
| SHAWANGUNK GRIT | WAVERLY BEDS |
| *E. maria Clarke | E. approximatus Hall & Clarke |
| BERTIE WATERLIME | COAL MEASURES |
| *E. remipes DeKay | E. mazonensis Meek & Worthen |
| *E. lacustris Harlan | E. mansfieldi C. E. Hall |
| *E. lacustris var. pachychirus Hall | E. pennsylvanicus C. E. Hall |
| *E. dekayi Hall | E. potens Hall |
| E. stylus Hall |
Eurypterus remipes DeKay
Eurypterus remipes DeKay. Ann. N. Y. Lyc. Nat. Hist. 1825. 1:375, pl. 29
E. remipes DeKay. Ibid. 1828. 2:273
E. remipes Harlan. Geol. Soc. Penn. Trans. 1832. 1: 96, pl. 5
E. remipes Bronn. Lethaea Geognostica. 1: 109, v. 9, fig. 1
E. remipes Hall. Palaeontology of New York. 1859. 3: 404*, pl. 80, fig. 1–12; pl. 80A, fig. 1–6; pl. 83B, fig. 2
E. remipes Clarke. Zittel's Text-book of Palaeontology, Eastman Translation. 1900. v. 1, pt II, p. 676, fig. 1420, 1421
and of numerous authors.
Not
E. remipes Eichwald. Soc. Imp. des Naturalistes de Moscou. Bul. 1854. 1: 49, 100, pl. 1
E. remipes Nieszkowski. Arch. für Liv-, Est- u. Kurland. 1859. Ser. 1, Bd. 2, p. 299–344, T. 1, 2
E. remipes Logan. Geology of Canada. 1863. p. 354, fig. 464
E. remipes F. Roemer. Lethaea Palaeozoica. 1876. pl. 18, fig. 4
E. remipes Gerstäcker. Klassen und Ordnungen des Thierreichs. pl. 35, fig. 13–16; pl. 43, fig. 1, 2
E. remipes McMurrich. Text-book of Invertebrate Morphology. 1894. p. 433, fig. 198
Description. Body of small size, ovate-lanceolate in form, four times as long as wide, relatively wide in front and broadest at one third of its length; moderately convex.
Cephalothorax relatively small. The carapace occupies one sixth or less of the total length of the body, is typically trapezoidal in outline, length to width as 3 : 4 or more frequently as 4 : 5; its lateral margins nearly straight, slightly converging forward, forming an obtuse, slightly rounded angle, with the nearly straight frontal margin. The posterior margin is broadly concave, the postlateral angles truncated, the truncated portion forming a distinct angle with the extremities of the concave part. The surface is moderately convex, highest in the middle near the posterior margin, where it is about one fourth as high as long. The carapace is bordered by a steeply inclined smooth marginal rim, broadest in front and narrowing toward the postlateral angles. The outer edge of the carapace is sharp; its underside is formed by the narrow doublure to which the connecting membrane is attached. The latter is frequently cleft along the anterior median line. Its width and natural position are shown in plates 5 and 6, figure 2. The compound eyes are situated a little in front of the middle, twice as far apart as distant from the lateral margin, one fifth, or less, as long as the carapace, bean-shaped, prominent, the kidneyshaped visual area entirely smooth. The two ocelli are situated on separate tubercles in a line connecting the centers of the compound eyes. Along the posterior half of the middle line a broad flat ridge (glabella) is delimited by two parallel furrows. Another pair of broader and deeper furrows passes in front and outside of the lateral eyes. These can be traced to the posterior margin, toward which they converge and become fainter. The part of the carapace outside of this furrow is very smooth. Frequently a small triangular area or a median furrow is observed on the mediofrontal part of the carapace.
The preabdomen occupies one fourth of the length of the body, and is a little wider than long. It attains its greatest width at about the fourth tergite. In the best preserved specimens it is almost evenly convex [pl. 5, fig. 5], the marginal portions but slightly flatter than the rest; in many partly compressed specimens [pl. 4, fig. 4] the axial part remains prominent, as in the axis of the trilobites, while the lateral parts assume an aspect similar to that of the pleura. They are depressed and slightly raised toward the margin and bent specimens show on the inner side folds that are slightly curved and pass obliquely forward. The first tergite is narrower than the others and its postlateral angles truncated like those of the carapace. Its length is about seven and one half times the width. The middle portion of the tergites is broadly arched forward, while the lateral portions are normal to the axis of the body or again curve forward. The antelateral angles are produced into articulating lobes. The tergites overlap along their anterior margins about one sixth their length. The posterior doublure is about one fifth the length of the segment. The ventral side of the preabdomen appears to have been more convex than the dorsal, for in compressed specimens the edges of the ventral plates project on both sides beyond the dorsal plates [pl. 4, fig. 4]. Probably the ventral median line was somewhat depressed, as in E. microphthalmus. The five sternites are longer than the tergites, medially cleft, bounded by straight transverse anterior and posterior margins and, with the exception of the operculum, are furnished with large rounded antelateral lobes. The operculum is longer than the other sternites, its antelateral angles are rounded off, while the anterior edge is produced into a broad median lobe. A like lobe is observed on the second sternite in the female. The postmedian angles of the two opercular plates are also produced into lobes, while those of the following sternites are well rounded.
The postabdomen is one third as long as the whole body. From the first to the sixth segment the width decreases by three fifths of the width of the first segment, while the length of the last is double that of the first. The first differs in appearance from the others in having the lateral margins strongly convergent backward, thus resembling the preceding tergites, while the others have subparallel lateral margins. Likewise the first segment has broadly convex anterior and equally concave posterior margins, while the succeeding segments have approximately straight transverse margins. The segments possess faintly outlined pleural areas denoted by a flattening of the lateral region, and a small spine on the postlateral angles. The spines of the last segment are distinguished from the others by their size, but do not grow into the long lobes which flank the telson in other species of Eurypterus. The posterior doublures are short, not one fourth as long as the segments.
The telson is short, having one fourth the length of the body, contracts rapidly from the articulation to one half its width and then continues slender to the bluntly triangular point. The margins are marked by oblique fine incisions that increase in size posteriorly and form a tuft of spines surrounding the point. The upper side is flat or slightly concave, the underside furnished with a rather narrow, flat-topped carina.
Appendages. The appendages of the cephalothorax with exception of the chelicerae were well known to Hall. They agree in all features with those of the closely related E. fischeri. The preoral appendages have been found more or less entangled with the endognathites; a single detached chelicera, lacking only the basal segment has however been observed [pl. 7, fig. 1]. The pair of pincers is broadest at the base, about twice as long as broad; the blades occupy only about one third of the length of the pincers; they are broadest at the base, taper rapidly, are edentulous, and with very acute tips. The tip of the movable blade is bent inward and is needlelike. The endognathites are relatively short and robust; of the first pair only the terminal spines or claws project beyond the shield border, while the members of the second pair extend for about one half their length beyond it, and those of the third pair clear it by fully three fourths their length. The fourth pair reaches beyond the third by the length of its last three segments. The first three pairs are of equal width, and in the first, the segments are twice as wide as long. The spines are long, slender, curved, paired and of subequal length, each segment bearing one pair [pl. 7, fig. 3]. The hooklike long, reflexed evagination of the fifth segment of the second endognathite in the male which has been described by Holm [text fig. 32] has not been seen in our material, probably because, as in Limulus, only the mature individuals after the last molt possessed it. Besides the long paired spines, each segment was furnished with one or more short, blunt spines [pl. 7, fig. 2], located at the anterior margin. The clawlike terminal segment and the spines of the penultimate segments are shorter than the others. As in most Eurypteri, the fourth endognathite lacks the spines, except those of the last two segments, and is relatively longer and more slender. As none of the coxal segments of the first three pairs of endognathites have been found detached, we are unable to describe them beyond stating that they are short and broad and bear at the inner upper angles, dentate manducatory faces with short conical teeth. They apparently show the progressive changes in form posteriorly as described by Holm. The coxa of the fourth endognathite is seen on plate 7, figure 6. Its length and width are nearly equal, while in the preceding coxae the width surpasses the length. The manducatory edge is borne on a marked prolongation. The circular foramen of the posterior margin, to which an auditory function has been ascribed, is well shown. Plate 4, figure 2, shows the mode in which the coxae of the endognathites are arranged like the tiles of a roof, exposing in ventral view only the upper margin and the prolongation bearing the manducatory edges, while plate 4, figures 2, 3, show the relative length and thickness of the endognathites.
The swimming legs are strongly developed in this type. When reflexed, they reached to the sixth tergite, and are correspondingly stout. The coxa is usually well exposed [pl. 6, fig. 8; pl. 7, fig. 7, 8]. It is subquadrate, broader in front than behind; the manducatory face is about one third the length of the inner margin and borne on a well defined neck. The face consists of a beveled chisel-like upper half followed by a more prominent row of six to seven denticles that are shorter than those of the other legs [pl. 7, fig. 6]. The second and third joints are short and ringlike. The stemlike process by which the second joint articulates with the coxa is distinctly seen in plate 7, figures 7, 8. The fourth segment is about one third longer than wide, distinctly convex forward and furnished with a small spine at the posterior end of the gently concave distal margin. The fifth segment is subquadrate, deeply emarginate at the under side of the distal extremity [pl. 7, fig. 8] and furnished with a triangular process on the upper side. The sixth segment is semioval, rapidly expanding distally and bearing an acute articulating process on the distal extremity. The seventh and eighth segments are much expanded; the seventh subrectangular, its anterior side very convex, the posterior nearly straight. The triangular guard plate is of relatively large size, its distal margin finely serrate. The eighth segment is oval in outline, about as long as the seventh, but only half as wide. Its anterior margin is very finely serrate, the serrae becoming longer and narrower toward the extremity and grouped into larger serrae, alternating with about six small ones [pl. 7, fig. 11]. The latter segment bears the small, oval, rudimentary ninth segment.
The epicoxite has not been seen in position; a detached epicoxite, found in association with this species and presumably belonging to it, is reproduced on plate 7, figure 5.
The endostoma has not been seen.
The metastoma is oval, not quite twice as long as wide, widest in the middle, or a little in front of the middle. The anterior extremity is gently emarginate and the posterior truncate.
The genital appendages of the species have been found well developed in but very few specimens, obviously owing to the fact that the great majority of individuals in the Litchfield region are immature. A mature female operculum with appendages, except for the terminal pair, is shown in plate 8, figure 1. The most important features of this specimen are the two pentagonal anterior pieces separated by sutures from the two halves of the operculum, and the two imbricating unpaired lobes, each of which expands slightly at the posterior extremity and terminates with two diverging, acute lateral lobes. The two tubular organs which were first recognized by Holm in E. fischeri, are here seen as two black curved appendages of the anterior part of the large median lobe. According to Holm they are tubular, thick skinned organs on the inside of the operculum. The tubes, in this specimen an internal view of the operculum, terminate exactly in the posterior corners of the pentagonal pieces, thus seeming to verify Holm's inference that they emptied there. This operculum also distinctly shows the transverse median line, which here is not simply constituted of a row of scales but begins as a sharp continuous linear depression along which the anterior part projects above the posterior, dying out toward the lateral edges. The posterior paired hornlike appendages are as in other members of the genus.
The appendage of the second sternite has not been seen separately, but its two long and slender terminal pieces are sometimes noticed below the appendage of the operculum in an interior view of the ventral side. Plate 8, figure 4, is a separate second sternite with the basal portion of its genital appendage preserved.
The male appendage has been observed in several individuals. It is best seen in the two detached half opercula [pl. 6, fig. 7] as a small median lobe with sagittate anterior and straight transverse posterior ends.
Ornamentation. The carapace exhibits a fine granulation along the lateral and frontal margins [pl. 6, fig. 3, 4] in a belt that is narrowest on the sides and widens in front so that it reaches back to the compound eyes; and a short transverse row of small spines along the posterior edge. The tergites possess a zone of small subcircular scales along the middle portion of the frontal margin and a transverse row of six longer spinelike scales along the posterior margin, which [pl. 8, fig. 2] are seen to be the posterior terminations of longitudinal rows of smaller scales of the general character. On the postabdominal segments [pl. 8, fig. 5] these terminal spines die out, but the six longitudinal rows of scales become reduced to two, which are very prominent, diverge backward, are circular at the beginning, lengthen posteriorly and finally overlap. A transverse row of small semicircular scales delimits the exposed portion of the tergites and postabdominal segments from the frontal overlapped portion. The ventral side [pl. 8, fig. 3] is ornamented with closely arranged semicircular to semilunar scales, largest and most prominent in the middle anterior region of the operculum, otherwise rather faint.
Ontogeny. Eurypterus remipes has not yet afforded any growth stages as young as those of species from Otisville. The smallest specimens are already of neanic age. Hall figured an example [1859. v. 1, pl. 80, fig. 1] which without the telson spine, measures but 18 mm. An outline drawing [text fig. 33] and photograph [pl. 4, fig. 1] of this specimen are here reproduced, and also the drawing of another small individual
 Figure 33 Outline camera drawing of young of Eurypterus remipes. ×3. The same specimen is reproduced on plate 4, figure 1 |
 Figure 34 Another very young specimen of the same species. ×3 |
[text fig. 34] given by Clarke in Zittel-Eastman, Text-book of Palaeontology, 1896, figure 1420. In the explanation of these figures Clarke pointed out the strongly anterior position of the eyes, relatively large size and length of the swimming legs and abrupt posterior contraction of the abdomen. The paucity of abdominal segments in figure 33 proves on investigation to be only apparent and due to the forcing of the posterior abdominal segments under the anterior. This secondary contraction of the body, apparently but accidental, or incidental to the process of molting, is also observed in some other young individuals. It is the principal cause of the contracted appearance of the abdomen.
We add here several more photographs of parts of very young individuals, among them a carapace [pl. 5, fig. 1] that is much smaller than any others before mentioned (2.5 mm long). This is especially remarkable for the great size and prominence of the compound eyes, as well as of the ocellar mound, a feature that was uniformly observed in the nepionic eurypterids from Otisville. The eyes are here 1 mm long, or four tenths the length of the carapace as against one fourth or 2.5 in the mature individual. This relatively great size of the eyes in youth is still apparent in larger individuals, as that figured in plate 4, figure 4. While these eyes of the young are relatively larger than those of the adult, they still remain entirely in the anterior half of the carapace, thereby producing an appearance of more anterior position which, however, in the figure cited from Zittel-Eastman is somewhat exaggerated.
The outline of the carapace in the youngest specimen is still rounded at the antelateral corner, but soon becomes squarish as in the older ones [pl. 5, fig. 1, 2]. The carapace itself is distinctly larger in comparison to the whole body than in the ephebic stage, although on account of the distortion of one or another part of the body in every observed individual it is difficult to demonstrate this fact by measurements. In specimen plate 4, figure 1, the smallest whole individual observed, the carapace occupies fully one fourth of the whole body, while in the larger specimens it is less than one fifth the length of the body.
The swimming leg when reflexed will reach to the tenth segment or farther in young individuals [pl. 4, fig. 1–3], while in the ephebic stage it reaches only to the seventh segment. The posterior endognathites appear also to be slightly longer.
It is questionable whether the preabdomen is relatively shorter in the young at our disposal than in the adult although the Otisville material indicates that in the nepionic stage the preabdomen may well have been shorter and more abruptly contracted toward the postabdomen. In the specimens before us, however [pl. 4, fig. 1–3], the relatively greater size of the carapace produces the impression of a relatively smaller and shorter preabdomen, since the latter is here only as long as the carapace, while in the resulting adult it is longer by one fourth.
The postabdomen in the young exhibits its usual proportions.
The ornamentation of the dorsal side shows a difference between the neanic and ephebic forms in the recognizable number of longitudinal series of scales, the former possessing but four on the anterior preabdominal and two on the following segments as against six and two in the ephebic stage.
Measurements. A well preserved and normal specimen, plate 5, figure 5, gives the following figures: length and width of carapace, 18.7 mm and 24.5 mm; length and width of preabdomen, 27.3 mm and 27 mm; length of postabdomen, 40.4 mm; its anterior and posterior widths, 20 and 7 mm. The telson measures 28 mm and is 5 mm wide at its beginning. The lateral eyes of this specimen are 5 mm long and 5.5 mm from the frontal margin. The first tergite is 3.6 mm long and 25.5 mm wide, the third about 6 mm long and 27.4 mm wide. The first postabdominal segment is 6 mm long and 19 mm wide in the middle, the last measures 10.5 mm by 8.5 mm.
The largest carapace observed is 50 mm in length and 67 mm in width; the one figured on plate 6, figure 3 is 45 × 60 mm.
Horizon and localities. DeKay's type of this species came from Waterville, town of Westmoreland, Oneida co., N. Y. Hall's numerous originals were partly from the same locality and in still greater number from Jerusalem or Wheelock's hill, Litchfield, Herkimer co., N. Y. which, with its neighborhood, has to this day furnished the principal supply of this species. In late years it also has been obtained in great numbers a few miles northeast (near Cedarville) and west (Paris Hill) of Jerusalem hill. It occurs near Oriskany; at Cayuga junction, Cayuga co. and possibly at Buffalo. In all these localities it has been found in the uppermost part of the Bertie waterlime, near the overlying Cobleskill limestone. But we have also from Seneca Falls, Seneca co., typical specimens from the Rondout waterlime above the Cobleskill limestone.
Remarks. As E. remipes was the first described representative of the genus and is a very close relative of the Baltic form, it is not surprising that the latter was for a long time identified with our species, until Eichwald [1860, p. 1355] pointed out the differences. Schmidt has more fully stated the relations of the two. He writes [op. cit. p. 62]:
Die amerikanischen Arten E. remipes DeK. und lacustris Harl. stehen dagegen unsrer Art ganz besonders nahe und es ist kein Wunder, dass man sie lange mit ihr identificirt hat. Sie kommen genau in dem nämlichen geologischen Niveau vor und könnten ganz gut als lokale geographische Varietäten unsrer Art angesehn werden. Der Kopfform nach steht unsre Art ziemlich in der Mitte zwischen den beiden amerikanischen, doch ist bei letztern die bei uns gewöhnliche trapezoidale Form selten so ausgeprägt. Auch das Metastoma weist einen kleinen Unterschied auf, indem seine grösste Breite bei unsrer Art in die Mitte, bei den amerikanischen etwas vor dieselbe kommt. Die grössere Zahl der Schuppenreihen auf der Oberseite bei unsrer Art, auf die Eichwald aufmerksam macht, scheint mir kein ganz genügendes Kennzeichen zu sein. Am meisten scheint sich der Schwanzstachel von dem der amerikanischen Arten zu entfernen, da er bei keiner derselben so schlank wird; ebenso ist auch das letzte Leibesglied bei den amerikanischen Arten am Grunde nie so tief eingeschnitten wie bei unsrer, bei der in dieser Beziehung allerdings auch Variationen vorkommen.
We may add a further difference, readily noticed with good material, namely, that the spines of the endognathites do not differ on the anterior and posterior sides so greatly in length as in E. fischeri, where the posterior spines are much longer than the anterior ones. Also the surface sculpture differs, as pointed out by Eichwald, but doubted by Schmidt, in that in E. remipes and lacustris there are seen distinct rows of scales in single file on the postabdominal segments while in E. fischeri only longitudinal patches of scales appear.
Other differences are seen in the form of the segments of the legs. Thus the fifth segment of the swimming leg is deeply concave on the underside in our species, but not so in E. fischeri, and the seventh segment is straight on the posterior side and very convex on the other, while it is equally concave on both sides in E. fischeri. A very suggestive distinctive character appears to us to be the great difference in the relative sizes of the compound eyes. In E. fischeri they reach about one third the length of the carapace, but in both E. remipes and E. lacustris they are but one fifth or less of the length of the carapace. For this reason E. fischeri makes a rather youthful impression when compared with our forms. Altogether, the differences are so small that Schmidt's suggestion that they are but geographical varieties, is fully supported.
The relations of E. remipes and E. lacustris are described under the latter species. It may be here stated that the two are more closely related to each other, than either of them to E. fischeri, indicating that they had but lately separated. Their differences rest mainly in the shape of the carapace and they are duplicated by those between E. fischeri and E. laticeps, two forms associated in the same (Baltic) rocks.
The E. pittsfordensis described by Sarle from the Pittsford shale, is also very closely related to E. remipes and lacustris, indeed is hardly more than a mutation and therefore undoubtedly a direct ancestor of the two later Bertie waterlime species.
Several of our specimens of E. remipes are so favorably preserved that they present features not observed before. The most important of these is that represented in plate 6, figure 6, which comes from a porous bed of coarse dolomite at Morganville, N. Y., in which the integuments are but little or not at all flattened. It shows a distinct glabella, corresponding in form and extension to that of Limulus and obviously due to the same causes. The same specimen also exhibits a deep furrow surrounding the lateral eyes and an obscure broad ridge connecting the latter and bearing the ocelli. The frontal slope is even and uniform and a narrow flat or slightly depressed border is found inside the beveled edge. Another partially compressed specimen [pl. 6, fig. 5] exhibits the glabella and a broad smooth border, corresponding in extent to the underlying frontal membrane of the underside of the carapace.
Another interesting specimen is that reproduced on plate 5, figure 7 which shows two circular, transversely wrinkled patches behind the frontal margin.
Specimens plate 5, figures 3–5, show a trilobation of the abdomen on account of the distinct depression of the epimera. It will be noticed that the spines on the posterior margins of the tergites are restricted to the axis. Where the body is slightly bent, as in specimens figures 3 and 4, peculiar oblique folds appear, which indicate the relative thinness of this part of the integument and may correspond to folds that formed during the life of the animal. This condition gives the test a peculiar trilobitelike appearance.
We have already mentioned among the differential characters of E. remipes and E. fischeri the double series of scales on the dorsal side of the postabdomen. In specimens where the inside of this integument is exposed, it is seen that between these rows the carbonaceous film appears lighter, suggesting a somewhat thinner test, which at the same time projects a little. This fact indicates that the interspace marks the position of the alimentary canal, the scales being the attachment places of the suspensory muscle strands. The interspace would then correspond to the projecting preanal ridge on the last segment in Pterygotus, which is also attributed to the pressure of the intestine.
Another specimen worthy of notice is one in which the test of the carapace is partially weathered, leaving the cast of the interior surface of the frontal part exposed and exhibiting a faint radiating structure that is restricted to the region where, from analogy with Limulus, the liver must have been located. It resembles strikingly the supposed liver impressions seen in some trilobites.
Eurypterus lacustris Harlan
Eurypterus lacustris Harlan. Geol. Soc. Pennsylvania Trans. 1834. 1: 98, pl.5
E. lacustris Hibbert. Roy. Soc. Edinburgh, Trans. v. 13, pl. 12
E. remipes Bronn & Roemer. Lethaea, 3d ed. 1854. 2: 666, pl. 91, fig. 1
E. lacustris Hall. Palaeontology of New York. 1859. 3: 407*, pl. 81, fig. 1–11; pl. 81A, fig. 1; pl. 81B, fig. 1–5; pl. 83B, fig. 3
Not
E. lacustris Salter. Geol. Soc. London. Quart. Jour. 1859. 15: 235
E. remipes Logan. Geology of Canada. 1863. p. 354, fig. 464.
Description. Body medium sized, ovate-lanceolate in form, robust, not quite four times as long as wide.
Cephalothorax broad and short. Carapace trapezoidal, about two thirds as long as wide (length: width as 6 : 9–10), occupying between one fifth and one sixth of the whole length; broadest at the base. Its lateral margins are nearly straight, slightly converging forward; anterior margins gently convex forward; antelateral angles well rounded; posterior margin slightly concave, bent forward near the genal angles. Profile of carapace not observed. The lateral eyes are small, only one fifth as long as the carapace or less; situated in front of the middle, twice as far apart as distant from the lateral margin, bean shaped, prominent; ocelli situated midway between them.
The preabdomen occupies about one fourth the length of the body. It is slightly wider (about one eighth to one ninth) than long, widening gradually to the fourth tergite and then decreasing again as gradually. The first tergite is seven and one half times as wide as long, the fourth only about six times. The outline of the tergites is the same as in E. fischeri. The sternites are also like those of that species, about four times as wide as long.
The postabdomen occupies one third of the length of the whole body. The first two segments contract at the same rate as the posterior preabdomen, the rest more gradually to nearly one third its anterior width. The telson corresponds in its relative size and character to that of E. remipes.
Appendages. The cephalothoracic appendages, including the chelicerae, are well shown in several specimens. They differ but slightly from those of E. remipes.
The chelicerae are seen in position in one specimen. The pincers are partly lost and partly obscure, but the full length of the basal joints is shown. A well preserved chelicera exhibiting a broader free blade with slightly curved tips and a narrower straight finer blade is shown in another example. The basal joint is twice as long as the blades and rather slender. This chelicera measures about three sevenths the length of the metastoma. A third detached chelicera, finely exhibiting the blades, is reproduced in plate 12, figure 1. Here the basal joint is broad and relatively short.
The four pairs of endognathites do not differ from those of E. remipes. The first three pairs are relatively short and stout; they increase in length from the first to the third pair at such a rate, that in their usual position their extremities form a straight line nearly tangent to the front of the carapace [pl. 10], the third being about twice as long as the first. The middle segments of the first endognathite are about one third wider than long, those of the third as long as wide. The spines of these endognathites are long and slightly curved and those of the posterior sides slightly longer than those of the anterior. The fourth pair of legs is longer than the preceding pair by one half and slightly more slender. The last clawlike segment is very strongly developed. The coxa of none of these endognathites has been seen fully exposed; nor has the epicoxite been observed.
The swimming legs are broad and powerful organs, though subject to some variation [see var. pachychirus]. They reach to the sixth tergite when reflexed. The coxa [pl. 11, fig. 5] is correspondingly large and strong. In form it does not differ from that of E. remipes. The second to the sixth segments are also like those of that species. The seventh segment which with the eighth forms the paddle is much widened and trapezoidal in outline; its length and width about equal; the posterior side straight or slightly convex, the anterior highly convex, the distal margin straight, with a large subtriangular guide plate for the eighth segment attached to it. The eighth and ninth segments are as in the preceding species.
The metastoma is very similar to that of E. remipes, but subject to some variation and frequently somewhat contracted in the posterior portion [pl. 11, fig. 5], giving it a more slender appearance.
The female genital appendage was very correctly figured by Hall [loc. cit. pl. 81B, fig. 4]. Several well preserved specimens before 
Figure 35 Eurypterus lacustris Harlan. Cast of interior of proximal portion of female opercular appendage us show the great size attained by this organ in mature individuals. It reaches with the long paired, hornlike terminal appendages, to the posterior edge of the third sternite. The interior tubular appendages of this organ are finely seen in the original of plate 12, figure 2, where the integument has broken away. They have the precise form and relative proportions of that of E. remipes. The appendage of the second sternite has not been seen unobscured by the overlying appendage of the operculum. It is, however, well shown in the interior view, reproduced in plate 11, figure 4 
Figure 36 Eurypterus lacustris Harlan. Young individual. Reproduced on plate 11, figure 1. Natural size [Hall's type of pl. 81, fig. 6]. It is extremely slender and pointed and reaches nearly as far back as that of the operculum. The male appendage does not differ from that of the preceding species.
Ornamentation. As far as our observation goes, the ornamentation is quite like that of E. remipes. This is especially notable in regard to the series of scales on the dorsal side, already correctly figured by Hall [pl. 81B, fig. 1]. The smaller scales which are rarely seen, are crescent-shaped to subtnangular and nowhere densely crowded. Those of the longitudinal series were larger and circular in the anterior portion, becoming elongate in the posterior part of each row.
Ontogeny. But little is known of the ontogeny of this species as but very few young individuals have been obtained and these are too far developed to afford much information. Hall's figure, [plate 81, figure 1], represents about the youngest stage known as yet in an entire specimen. This is here reproduced by photograph on plate 11, figure 1 [text fig. 36]. This specimen exhibits the somewhat larger size of the eyes and the more compact form of the body. It must, however, be remarked that the body shows evidence of compression axially.
Measurements. In a well preserved adult the carapace measures 44 × 63 mm; the preabdomen (slightly shortened) 51 × 72 mm; the first segment measures 8.8 × 65 mm; the fourth 11 × 70 mm; the postabdominal segments measure respectively 8 × 51 mm; 12.7 × 42 mm; 14.5 × 37 mm; 15 × 33 mm; 17.5 × 27.5 mm; 20.5 × 22 mm. The eyes are 4.7 mm long. The telson spine is 64 mm long and 12.5 mm wide at its anterior extremity. The fourth endognathite projects 41.5 mm beyond the edge of the carapace, the swimming leg 70 mm. In another specimen the carapace is 49.5 × 71 mm; the preabdomen 60.5 × 80.5 mm; the postabdomen is 88 mm long and measures 56.5 mm at its anterior extremity and 20 mm at the posterior one. The telson is incomplete. The eyes are 8.5 mm long; the first endognathite projects 8.5 mm; the second 13 mm; the third 21.5 mm; the fourth 35.5 mm; the swimming leg is 75.5 mm long.
Horizon and localities. E. lacustris occurs typically only in the Bertie waterlime quarries at Williamsville and Buffalo, N. Y. and Bertie, Ontario. A few smaller specimens also have been obtained at Black Rock, Erie co. and Union Springs, Cayuga co.
Remarks. In regard to the differences between E. remipes and E. lacustris, Hall makes this statement: "This species differs from E. remipes in its greater size, and less abrupt attenuation toward the tail, while the carapace is proportionately broader and shorter. There are likewise differences in the anterior feet, and in the form of the postoral plate; the entire form of this latter appendage not having been fully determined." We see the principal distinctive character in the greater width of the carapace, the proportion of length to width in E. remipes being as 6 : 7 (with 8.5 as maximum) and E. lacustris as 6:9 (8.5–10); and in the different outline; the former having a squarish carapace with subparallel sides and straight frontal margin and subrectangular anterior angles, while in the latter species the sides are more convergent and the anterior angles more rounded. Specimens are, however, common which it is difficult to assign to either species, partly on account of their original intermediate form and partly because of secondary changes through lateral compression. The average representatives of E. lacustris are considerably larger than those of E. remipes although a few carapaces of the latter species indicate that it did not fall much short of the other type in size attained. Nevertheless the great majority of the specimens of E. remipes obtained in the central New York region are very much smaller. No differences have been observed in the proportions of the abdomen and the appendages (including the metastoma), save perhaps the swimming legs, in which a tendency to greater broadening is observable in E. lacustris, and this has led to the variety pachychirus.
A variety robustus of the present species has been distinguished by Hall, in regard to which it is stated that: "The form of the anterior feet and the swimming feet are essentially the same, while the joints of the body are proportionately longer and stronger, furnishing sufficient ground for a variety, but not satisfactory evidence of specific difference." In the explanation of his figures [plate 81C] a note is added saying that further examination with other species has shown that the form has the characters of a distinct species. The difference supposed to rest in the greater length and strength of the abdominal segments is due to the postmortem separation of the segments as far as the stretching of the connecting membranes permitted, while on the other hand, Hall's types of E. lacustris are all somewhat contracted through sliding of the segments over each other. We have been unable to find other differences and therefore consider robustus as only a preservation state.
Eurypterus lacustris Hall var. pachychirus Hall
Eurypterus pachycheirus Hall. Palaeontology of New York. 1859. 1: 412*, pl. 82, fig. 1–3
This variety which Hall separated from E. lacustris is based on an abdomen, a group consisting of two swimming legs, several endognathites with operculum; and a separate swimming leg. The types of the abdomen and the swimming leg are in the State Museum; the group of swimming legs and operculum in the American Museum of Natural History. The species is diagnosed as follows: "Carapace unknown. Body robust: crust thick; articulations strong, those of the abdomen extended in strong salient angles at the lateral edges. Bases of the anterior feet strong and broad. Swimming feet strong and large; the seventh (sixth) joint very large and long, inflated and much curved on the anterior side; the free eighth joint is thick and strong, somewhat oval, and narrowing gently toward the point of articulation; the terminal palette is small. The last joints (and perhaps the others) of the swimming feet are serrated on the margins."
In the notes it is added that "the peculiar arching of the seventh (sixth) joint, and the thickened or inflated character of the swimming foot in this species, appear to be sufficiently characteristic to rely upon for specific distinction," and as further distinctive characters are mentioned, that the scaly surface marking of the body is more strongly developed than in any other species observed, and that the anterior margin of each segment is raised in a little elevated band, more prominent and more strongly serrate on its anterior edge than in any of the other species, and finally that the surface is marked by strong longitudinal wrinkles somewhat irregularly disposed.
The great width of the distal portion of the swimming leg and especially that of the seventh segment appear as good distinctive characters, when compared with the narrower appendages of the typical lacustris, but a survey of the larger collection of specimens since gathered from the Bertie waterlime of Buffalo leaves no doubt that there are numerous examples with equally broad swimming legs which are not otherwise distinguishable from E. lacustris and that furthermore there occur transitional forms between the two in this regard.
The additional characters, the stronger sculpturing, etc., are taken from the type specimen [op. cit. pl. 82, fig. 1] which also retains a swimming leg not shown in the figure. This specimen differs markedly in state of preservation from the great majority of the Buffalo specimens, in not being preserved in a black, perfectly attenuated film, but in bas-relief and with a light brown film, upon which the scales distinctly show. This different preservation is due to the conservation of the fossil, not in the mud rock of the typical waterlime, but in a lighter, dolomitic, slightly coarser grained, somewhat uneven bedded rock that contains Leperditia scalaris and Orthothetes interstriata. This forms the top stratum of the Bertie, at Buffalo, directly underlying the Cobleskill. There are two other specimens from this bed in the Museum of the Buffalo Society of Natural Sciences and one in the State Museum, all of which retain the surface ornamentation in like distinctness and one of which possesses the broad swimming legs of pachychirus; but in all other characters they are indistinguishable from E. lacustris, especially in regard to the carapace.
We have for these reasons here placed pachychirus with E. lacustris as a variety distinguished by its tendency to a broadening of the swimming legs, and consider the other distinctive characters cited by the author of the species as due to the preservation of the material. It may be added that the exposure of the elevated anterior band of the segments and of the line of scales at its posterior margin is due to a pulling of the integument before entombment.
Eurypterus dekayi Hall
Eurypterus dekayi Hall. Palaeontology of New York. 1859. 3: 411*, pl. 82, fig. 1
This species was based on a single specimen, now in the State Museum [pl. 20, fig. 1]. Its distinguishing characters are thus given in the original description: "The entire body is proportionally shorter, the carapace shorter and broader than in E. remipes. The swimming feet are shorter, and the terminal palette a little more developed than in E. remipes or E. lacustris, and the upper abdominal joints differ less from the thoracic joints in length, while the last one is alate on the two lateral edges, a feature not observed in any other species."
The aspect of the type is that of a specimen which has distinctly suffered contraction by a shoving together of the segments and, mindful of the strange changes in aspect resulting from a pushing or pulling of the segments, especially in cast-off integuments, one might reasonably infer that all the above cited differences, save the alate lateral edges of the last segment, were largely of casual origin. The other specimen figured on plate 19 which is more favorably preserved, exhibits the same and additional distinctive characters while it is clearly but partially contracted in the preabdominal region and distended in the postabdominal. The most striking new character in this specimen is the presence of four to five long spines on each segment of the endognathites, instead of but one or two in all other members of the genus. The combined evidence of the two specimens leaves no doubt that we have to regard E. dekayi a peculiar aberrant type of Eurypterus. The following are the characters of this species:
Description. Body of small size, short but broad and compact. The carapace is about one sixth the length of the body, the latter a little more than three times as long as wide.
Carapace relatively very broad and short, its length to width as 6 : 10–11; the character of the margins as in E. lacustris; the lateral eyes relatively small (one fifth of length of carapace), in front of center, far apart, halfway between median line and lateral margin. Ocelli not seen.
Abdomen. The preabdomen is contracted in both specimens, in the second less than in the type. Its length is to its width as 2 : 3+. It probably contracted more rapidly at the last tergites than the associated species of Eurypterus, but not so much as the two specimens, in which the last sternites are somewhat shoved together would indicate. The tergites have not been seen, except the first in the hypotype, specimen 2, where it is a narrow band, 11 times as wide as long. The operculum and other sternites apparently do not differ from those of E. lacustris except in being relatively somewhat wider.
In the type specimen the postabdomen occupies four ninths of the length of the body without the telson; it is about one fifth longer than wide at its beginning and its total length surpasses its anterior width by about one fifth. At the posterior extremity it has decreased to one third of its anterior width. The first segment is about four times as wide as long, the last is one seventh longer than wide. Its most striking feature is the long alae, resembling those of E. fischeri in relative size and form. Like the latter they were probably somewhat variable.
The telson spine occupies in the type but little less than one third of the length of the body, as against more than one fourth in the other species. Although the abdomen is contracted, it is manifest that the spine is relatively long. Otherwise it does not differ from that of E. lacustris. It is five times as long as its anterior width.
Appendages. But one (the third) endognathite has been seen, its last four segments projecting beyond the head shield. In the type the basal portions of all endognathites are withdrawn under the carapace and have been artificially exposed. The endognathite exhibits four spines on its fifth, five on its sixth and four on its seventh segment, all of which seem to be of uniform length and slender when compared with those of other species of Eurypterus. It seems hence, that in this species, not only the two usual spines at the distal edge are present, but also that the rudimentary spines at their bases, seen in other species and one or more accessory spines have grown out to the full size of the first pair.
The swimming legs are equally distinct from those of the associated Eurypteri in several features. The coxa is distinctly broader, corresponding to the great basal width of the carapace. Its length and width are subequal. The second and third segments are annular.[5] The fourth, fifth and sixth are notably stronger and wider than in E. fischeri and remipes, though not differing otherwise, while the seventh is remarkably short and wide, having the general form of the corresponding segment of E. lacustris var. pachychirus, but being much smaller relatively to the whole leg. The eighth segment also, forming with the seventh, the oar blade, is notably smaller than in other species. The terminal, rudimentary segment, as already remarked by Hall is a little larger than in E. lacustris.
The metastoma is like that of E. lacustris. The female and male appendages, seen in these specimens, do not appear to differ from those of either E. lacustris or E. remipes except that the terminal paired lobes in the female appendage are shorter than in E. lacustris and correspond to those of E. fischeri or remipes.
Ornamentation. Only interior views of the integument have been obtained and hence the character of the ornamentation has remained unobserved, except for the two converging rows of spines on the postabdominal segments and a few traces of subtriangular scales, indicating a sculpturing very much like in E. fischeri.
Measurements. The carapace of the type is 31 mm long and about 58 mm wide; that of the hypotype measures 33 × 55 mm; the eyes of the latter are 6.8 mm long. The preabdomen of the type measures 40.4 × 71 mm, both measurements being but approximate on account of contraction and imperfect preservation. In the hypotype the dimensions of the preabdomen are 42 × 63 mm. The postabdomen of the type is 50 mm wide at the proximal end, 56 mm long and 17 mm wide at the distal end. That of the other specimen is too long by distention, its proximal width being 50 mm, its distal 17.5 mm and its length 73 mm (probable normal length about 65 mm). The telson of the type is 53 mm long and 10 mm wide at its proximal end.
Horizon and localities. The two known specimens are from the Bertie waterlime of the neighborhood of Buffalo.
Eurypterus maria Clarke
Eurypterus maria Clarke. N. Y. State Mus. Bul. 107. 1907. p. 305, pl. 1, fig. 1, 2, 4; pl. 2, fig. 2, 4, 7; pl. 3, fig. 1–5, 7
The preliminary description of this form in Bulletin 107 is as follows:
The general form of the largest observed individuals of this species is elongate and slender with very little abdominal expansion and no lobation of the segments. In these ephebic conditions the head is somewhat elongate, regularly rounded in front and with subparallel lateral margins. The eyes are crescentic, subcentral, as far asunder as the inner margin of each is from the margin of the shield.
The ocellar lobe is well denned at an early stage. A specimen 63 mm long without the telson, apparently mature, has 11 segments, but a break across the body leaves room enough for a 12th. The width of the base of the head is 15 mm and this is but very slightly less than the greatest expansion of the abdomen. Little trace of surface sculpture is visible on any of the parts.
Description. Body. The body is terete or subcornical, with subcircular sections in all parts save the carapace. It is about five times as long as wide, and tapers very gradually from the base of the carapace.
Cephalothorax. The cephalothorax is broadly semielliptic to semicircular in outline, about one third wider than long, widest at the base and evenly rounded. While it is as broad as, or broader than, the widest part of the abdomen, it attains but one sixth to one seventh the length of the body. Its surface was evenly and highly convex, culminating near the center at the ocellar mound. It is surrounded by a narrow thickened filiform border. The posterior margin is straight transverse with a faint indication of fulcra near the acute genal angles.
The compound eyes are subcentral in position, situated as stated in the preliminary description; the visual surface is crescentic and only prominent in compressed specimens, while the entire ocular node, which has the form of a sector, being rounded at the outside and angular on the inner side, is distinct only in young individuals. The eyes occupy about one third the length of the carapace.[6] The ocelli are situated on a line connecting the centers of the compound eyes and located on a large, prominent mound.
Abdomen. The abdomen is slender, widening so little from the base of the carapace to the third segment that in many specimens it tapers with apparent regularity toward the telson. The length is three times the greatest width.
The preabdomen is widest at the third and fourth tergites. Its length is to its width as 5 : 4. The tergites are narrow bands with straight or but slightly curved transverse margins and parallel lateral margins. The anterior and posterior margins diverge near the lateral extremities where the segments widen somewhat. Their antelateral angles are produced into broad blunt lobes, while the postlateral angles are either rectangular or furnished with short acute lobes, that are directed posteriorly and increase somewhat in size in the posterior segments. The segments were originally highly arched with a narrow flat strip, representing the epimera, along the lateral margins. Each tergite was not only strongly bent from one side to the other but also from forward backward and highest in the anterior third, with a steep decline forward and a more gradual one backward, finally grading into a narrow flat border. The first tergite is considerably shorter than the others. It is six to seven times as wide as long; the following ones are about four times as wide as long.
The sternites are less straight bands than the tergites, their middle portion curving forward more distinctly. Their antelateral angles are produced into broad rounded ears or lobes, while the postlateral angles are well rounded. The operculum has not been observed.
The postabdomen tapers uniformly to the posterior extremity which is but one third as wide as the anterior. The segments are all circular in section, and they gradually become longer while they diminish in width, the first segment being four times as wide as long, while in the last the width is to the length as 3 : 4. The segmental rings are very simple with but very inconspicuous lateral flanges in the first segments and none in the last.
The telson is bluntly lanceolate; at the base it is three times as wide as long. Its dorsal side is convex and raised into a median keel; the underside flat and the lateral margins are furnished with sharp, bladelike edges.
Appendages. In spite of the great number of heads found only the swimming legs have been observed In mature specimens [pl. 21, fig. 11] these are remarkably short and protrude but little more than half the basal width of the carapace. The eighth segment (the palette) is long, elliptical, the ninth forming a small terminal claw. Of the seventh segment but a portion has been seen protruding from below the carapace and this indicates that it was considerably narrower than the following ones.
Ornamentation. No scales or tubercles have been made out on either the carapace or abdomen. The only traces of ornament observed are a median transverse line on both the sternites and tergites, with traces of more lines in the latter, especially near the anterior margin.
Ontogeny. In its ontogeny Eurypterus maria includes a larval stage that is not only strikingly different from the mature but also highly suggestive phylogenetically by its great similarity to Strabops. This we have identified with the nepionic stage since it can not be much older than embryonic. It is represented by the two specimens plate 21, figures 1, 2.
Herein the most striking differences from the ephebic stage are:
- The great width and small length of the body and the resulting rapid contraction from the preabdomen to the postabdomen.
- The excessive width and small length of the subtriangular carapace.
- The great size of the compound eyes.
- The shortness and great width of the segments.
- The relatively greater size of the swimming legs.
In these nepionic specimens the width of the body is to its length as 3:8, and in the ephebic stage as 3:15, hence the former stage is about twice as stout as the latter and conversely the contraction of the body is twice as rapid in the nepionic stage.
The carapace of the mature Eurypterus maria is one third wider than long (3 : 2), while that of the youngest nepionic specimen is twice as wide as long (4 : 2) and in the other much larger nepionic specimen the proportion is still 3½ : 2. The antelateral angles are so strongly truncated that the carapace approaches a triangular outline.
In this nepionic stage the compound eyes may reach one half the length of the carapace [pl. 21, fig. 3], while in the ephebic form they occupy only one third that length. They also lie farther forward and converge strongly on their longitudinal axes, while in mature individuals they either converge slightly or are subparallel. This strong convergence in the nepionic stage is continued into the neanic stage [pl. 21, fig. 9] and is in harmony with the convergence of the lateral margins. It is further to be noted that the outline of the ocular node is broadly elliptical in this stage and that the crescentic visual surface is not to be distinguished from the ocular node. It is therefore possible that the visual surface extended over the whole node and not until later became restricted to the crescent band or anterior side of this node. The appearance of these nodes as represented in figures 9 and 3 would seem to support this view. In the former specimen the eyes are not only circular, at least that on the left side which is fully exposed, but this left eye is also distinctly surrounded by a thickened border, and as this border in the adult only surrounds the visual surface, the inference is suggested by this specimen that the whole node was covered by the visual area. The second specimen suggests that here the visual surface still occupied the greater portion of the node, leaving only a narrow crescent on the inner side of the node unoccupied.
The shortness of the segments, compared with their width, is a striking feature of these nepionic individuals. The preabdominal segments are from 6–9 times as wide as long, while in the ephebic stage they are but 4 times as wide as long with the exception of the first tergite which retains the nepionic dimensions. The first tergite in the first nepionic stage, shows no difference in length from the others, while in the next stage [pl. 21, fig. 8], it is well distinguished. A specimen [pl. 21, fig. 1] with a length of 5.25 mm has but 8 segments. One [pl. 21, fig. 2] which measures 8 mm has already the full complement of 12. In the latter the shortness of the segments is still more striking than in the former and it appears that the insertion of the new segments took place rapidly in successive molts at the expense of their longitudinal growth. It is impossible in these young specimens to discern the boundary between the pre- and postabdomen.
The swimming legs are relatively longer and wider in the larval forms, as a comparison of figures, plate 21, figures 1 and 2; plate 21, figure 5, with plate 21, figure 11 will readily show. In the ephebic specimen the swimming leg when reflexed hardly reached beyond the third segment; in the first nepionic specimen it extends to the posterior margin of the fourth; in the second even to that of the fifth. The specimen, figure 5, also furnishes evidence of the greater size of this leg in the neanic or following stage.
The telson in the nepionic stage does not materially differ in shape and relative size from the mature condition.
Neanic growth stage. This stage is represented by a considerable number of specimens from which the originals of figures 3–11 have been selected. These specimens differ from the mature stage in the following characters:
- The carapace is still relatively wider though not as wide as in the preceding stage and already approaches a semicircular shape.
- The compound eyes are still relatively large, holding a median position in proportions between the nepionic and ephebic stages. In plate 21, figure 9 the length of the eyes to the length of the carapace is as 3 : 7, while in the nepionic stage they are as 3 : 6 and those of the ephebic stage as 3 : 9. They are also distinctly nearer to the frontal margin than in the mature specimens and the ocular nodes are more prominent than in later stages. They still show a distinct tendency to converge forward. The crescent visual surface is now distinctly seen, but it appears still broader than in the mature stage.
In many examples of this stage the ocellar mound is so large and distinct that its greater size and prominence in more youthful stages may be legitimately inferred [figs. 3, 4, 8, 10].
The abdomen in these neanic specimens is already as slender as in the adults [fig. 8]. One exception is the fine specimen [pl. 22, fig. 7], which is a little broader than the others. The presence of the lobes of the postlateral angles, however, indicates that this individual was flattened out before burial.
Measurements. Length of smallest nepionic individual, 5.25 mm; its width, 2 mm; width and length of carapace, 2 mm and 1.1 mm; length of compound eye, .45 mm; length of swimming foot, 1.6 mm.
An average specimen [pl. 21, fig. 12] measures in length (with the telson gone) 63 mm; its greatest width, 16 mm; the length of its carapace is 12 mm; that of the first segment 1.5 mm and that of the third 3.5 mm. The last segment is 6.5 mm long and 6 mm wide.
The largest carapace observed measures but 16 × 11 mm, so that this form is one of the small species of the genus.
Position and localities. Abundant in the fossiliferous shale of the Shawangunk grit at Otisville, N. Y.
Remarks. In aspect, Eurypterus maria is greatly different from all its American congeners. This is largely due to the terete form of the body that apparently is without preabdominal expansion. A few specimens [pl. 22, fig. 8] indicate that there was a slight expansion, but it seems to have found its expression mostly in an increased vertical convexity of the body. This convexity both of the dorsal and ventral sides producing the subcircular section of both preabdomen and postabdomen, is shown by several specimens which are but slightly compressed. A species quite similar to our type in both form of body and size is E. pygmaeus Salter from the Downtonian (uppermost Ludlow) of Great Britain. Its carapace, however, seems to have been a little longer
 |
| Figure 37 Eurypterus maria Clarke |
| I–V States of preservation affecting the outline of the carapace and the size and position of the compound eyes |
and the eyes a little more forward in position. From the other species of Eurypterus these two forms differ in their long, gradually tapering, terete body and the small size of the swimming legs.
The variability in the size and position of the eyes is commented upon in the preliminary description. Note might also be taken of the confusing variability in the outlines of the carapace. A survey of a great number of carapaces shows that the variability of features which in other species exhibit considerable stability, is for the most part due to the great convexity of the carapace of this species and the resulting various modifications under the influence of differing directions of compression. The accompanying text figures are inserted to illustrate this fact. In figure I the carapace has been vertically and gradually compressed so that the eyes are projected on the horizontal plane directly below their original position. The uninterrupted concentric wrinkles and the normal size of the eyes characterize this frequent mode of preservation. In figure II the vertical pressure has acted with a slight centrifugal component, the eyes have wandered outward and become long, narrow and slitlike while the wrinkles are only found parallel to the lateral margins. In the specimen figure III the reverse has taken place; a component acted in a centripetal direction and moved the eyes inward. In this case the latter always appear reduced in size, the whole change producing a strangely different aspect of the head, which is also frequently somewhat squarish in outline [pl. 22, fig. 1]. In this state of preservation the margin of the head is frequently cut by many radiating marks indicative of the intensive flattening out of the outer portion of the carapace. In figure IV the pressure acted from behind and the head is folded over forward and nearly always shortened. In figure V, the pressure acted obliquely, so that the left eye is completely flattened out and the other reduced to a narrow crescent. The possibility of so many different expressions of form under pressure must be taken into account in construing specific values.
Eurypterus megalops nov.
Description. Carapace semicircular (width of type, 45 mm, length, 30 mm), both frontal and lateral margins forming a continuous curve; posterior margin well preserved in the middle portion only, which is rather strongly concave; genal angles not clearly seen; eyes submarginal, of large size, occupying one fourth the length of the lateral margin, situated behind the middle line of the carapace; visual surface crescent-shaped (in compressed condition); eye surrounded on the outside by a distinct dumbbell shaped depression; ocelli well defined, large and lying between the anterior portions of the lateral eyes.
The ornamentation is obscured by the compression of the specimen; patches of the surface exhibit a shagreenlike sculpture which suggests that the better preserved fragments of integument with similar ornamentation, found in the same beds, belong to this species.
Horizon and locality. Frankfort shale (Schenectady beds) near Rotterdam Junction, Schenectady co., N. Y.
Remarks. This species is remarkable in several regards; mainly in the extraordinary size of the eyes, which in relative proportion are comparable to the eyes in larval stages. Their submarginal position and the round shape of the carapace give the form a distinct pterygotoid aspect, but the eye node and the visual surface are those of an Eurypterus. This species with its larval eyes and other features indicating the traits of a synthetic type promises, when better known, interesting data relating to the phylogeny of the eurypterids.
Eurypterus microphthalmus Hall
Eurypterus microphthalmus Hall. Palaeontology of New York. 1859. 3:407*, pl. 80A, fig. 7
Eurypterus eriensis Whitfield. N. Y. Acad. Sci. Ann. 1882. 2:196
Eurypterus eriensis Whitfield. Geol. Sur. of Ohio. 1893. 7:416, pl. 1, fig. 31, 32
Description. The entire animal is small, but robustly built. The cephalothorax is relatively large, its length equal to that of the preabdomen. The body is sharply divided into the broad, short preabdomen and the narrow, cylindrical postabdomen. While the carapace was slightly elevated, the segments of the preabdomen were strongly arched, increasing in hight posteriorly and the last four segments were circular in section. The carapace and the preabdomen together form a compact oval, at the narrow end of which the taillike postabdomen is inserted, the whole body much resembling a tadpole in its last stage. The integument of this form seems to have been relatively strong.
The carapace is semielliptic, approaching the semicircular form and outline; its length to width approximately as 2 : 3 and in older individuals approximately as 3 : 4. Its outline is evenly rounded. It is slightly prominent, reaching its apex between the lateral eyes, whence it rapidly declines forward and gradually backward.
A longitudinal triangular depression at the middle of the frontal margin indicates sometimes, in compressed specimens, the location of the frontal shield of the doublure. The lateral eyes are very small, kidneyshaped, and prominent, with vertical, semicircular visual surface and placed so much within the margins that the distance between them is not greater than that from the eye to the margin of the carapace, as pointed out in the brief original description. They are also placed relatively far forward, their posterior ends lying in front of the transverse middle line of the carapace. The ocelli are separate, very distinct, and placed on a line connecting the posterior angles of the lateral eyes. The doublure of the carapace is narrow, widening slightly near the postlateral angles.
No limbs are shown in our specimens.
Only the first tergite of the dorsal side is shown in the type specimen. This is relatively narrow. Another example retains the ventral integument of the abdomen. The operculum and the first sternite are deeply cleft, depressed and distinctly sutured along the middle line. The transverse lines are very distinct.
The telson has not been observed.
The carapace was smooth but on the sternites and postabdominal segments are traces of small tubercles. Whitfield has observed "minute spinelike pustules or pointed granules . . . . arranged in irregular transverse lines across the body." Along the posterior margin of the dorsal side of the last segments appear four or five longitudinal folds, originally probably spine bases.
Measurements. The carapace of the type specimen measures 15.5 mm in length and 22 mm in width. The eyes are but 2.5 mm long. Wrinkles and the direction of the eyes show that it has suffered a slight oblique compression. The best preserved carapace is from Litchfield. It measures 17.5 × 27.4 mm. Its lateral eyes are 3 mm long and 6.3 mm apart. A carapace from Cherry Valley measures 25.3 × 35 mm. The largest obtained in the state is 30 mm long and 45 mm wide. The type of the carapace of E. eriensis preserved in the Columbia University Museum measures 27 × 36.8 mm and a smaller cotype in the same collection, 24.5 × 32.4 mm. The proportions of the carapace hence lie between 2 : 3 and 3 : 4.
The tergite of the type is but 1.8 mm long. A nearly entire specimen from Onondaga Valley possesses a carapace 20.6 mm long; its preabdomen (perhaps somewhat pushed together) measures 26.5 mm and the remaining five postabdominal segments about 30 mm. It is widest at the second sternite (30.5 mm). The abdomen figured by Whitfield is complete to the telson, which is lacking. The specimen is probably slightly reduced in the figure, judging from the size of the accompanying carapace, and we have not the original at hand. The preabdomen in the figure is 31.5 mm long and about 33.8 mm wide. The postabdomen is 35.8 mm long and shrinks from a width of about 24 mm to 10 mm in the last segment.
Horizon and localities. The type came from a loose boulder near Cazenovia, Madison co., N. Y., which by its lithologic character and the associated fragments of Spirifer vanuxemi shows its derivation from the Manlius beds. Besides this rather poorly preserved specimen the State Museum possesses a series of carapaces and a nearly complete specimen of this extremely rare form. This entire specimen was found loose in Onondaga Valley by Prof. Philip F. Schneider and appears also to have come from the Manlius limestone. Of the carapaces, one was collected by the authors in the town of Litchfield in Manlius limestone, not less than 100 feet above the Eurypterus horizon in the Bertie waterlime; another was found loose on Jerusalem hill (probably also from Manlius limestone, according to the lithologic aspect of the slab); still another was obtained at Cherry Valley falls. A series of carapaces, some of relatively large size, were obtained in the layers of the Manlius formation at the Kolb farm, Crane's Corners, near Jerusalem hill, Herkimer co., and some segments in the waterlime of the Manlius at Manlius village. From this it appears that there is a continuous waterlime bed near the top of the Manlius formation, extending from Onondaga county to Albany county and the species seems to be confined to this layer. Professor Whitfield's types of E. eriensis came from the hydraulic limestones (Monroe formation) of Beach Point, Put-in-Bay Island, Lake Erie.
Remarks. E. microphthalmus is well characterized by a number of peculiarities, the most notable of which are the round outline of the head, the small size and subcentral position of the lateral eyes and the short compact form of the preabdomen, from which the cylindrical postabdomen is well set off. The slight compression of both the carapace and the abdomen shows that the integument must have been relatively very strong. To this fact may be also due the absence of the scales on the surface.
While the differences between the carapaces of E. microphthalmus and E. eriensis, cited by the author of the latter species, seemed well founded as long as the poorly preserved type of the former species or the not quite successful representation of the same were solely available, the specimens which have lately been collected in the Manlius limestone, leave no doubt of the identity of the Ohio specimens with E. microphthalmus. The proportions of the carapaces are the same, within the small variation due to different compression and to the developmental changes.
E. microphthalmus is, stratigraphically considered, an isolated form, since it is the sole eurypterid hitherto known from the Manlius limestone. It is likewise isolated from the preceding eurypterids by the series of peculiar features cited above as characteristic of this form, and though the form is in general outline near enough to the preceding E. remipes so that its derivation from that common species could be conceived, the fact remains that it is more closely related to later species, like E. brewsteri Woodward, from the British Old Red sandstone, with which it has in common the round outline of the carapace, the small size, forward and approximate position of the eyes—that is, all the features which give it its characteristic aspect. The Old Red species is also without ornamentation of the carapace. A third species exhibiting the same characters, except the lack of ornamentation, is E. approximatus Hall & Clarke, from the Waverly beds of Pennsylvania. These species form a well defined group that is distinctly foreshadowed by one of the eurypterids of the Shawangunk grit, viz, E. maria.
Eurypterus pittsfordensis Sarle
Eurypterus pittsfordensis Sarle. N. Y. State Paleontologist Rep't. 1902. p. 1098, pl. 10, fig. 7; pl. 15, fig. 1–3; pl. 16–23; pl. 24. fig. 2–5; pl. 25, fig. 2, 5, 6
Eurypterus pittsfordensis was very fully described by its author. We have secured little additional material since the Sarle collections were added to the museum and therefore reproduce the original description with our observations appended:
This species is comparatively rare and is not represented in the collection by any entire individuals. There is, however, sufficient material to enable its main features to be correctly determined.
The entire animal is large and robust, and broadest at about the third segment. The cephalothorax is two thirds as long as broad, eyes of medium size, appendages heavy. The preabdominal and postabdominal portions are not strongly differentiated; the telson long, probably equal in length to the five preceding segments.
The cephalothorax is broad, rounded in front, the sides curving out near the genal angles, and the base straight, or very gently curving over the middle portion, and extending a little forward near the sides. The margin is beveled in for a distance, in the average sized individual, not exceeding 2 mm in the widest part or in front, narrowing and fading out at the genal angles. The extreme edge is slightly upturned. The compound eyes are separated by one half the breadth of the shield, with their bases in line with its center. They are prominent, reniform, broader at the anterior ends, and one fifth as long as the shield. The ocelli are situated on a faint tumescence between the centers of the compound eyes. They are rather large and separated by about their own diameter. Near the basal edge of the shield is a pair of sharp, raised, triangular scales, one on either side of the axial line. In some cases there is a row of shallow, flat-bottomed pits on the beveled margin.
The abdomen increases slightly in breadth from the base of the cephalothorax to the third segment, then tapers to the telson, there being no apparent constriction between the preabdomen and postabdomen. The tergites are comparatively short, the length averaging a little less than one fifth the breadth. They are broadly concave along the middle of their posterior edges, and each carries, bordering this curve, four raised, triangular scales like the two on the posterior border of the cephalothorax and the middle two in line with them. The five sternites are medially cleft and marked by transverse sutures, which give to each the appearance of having been formed by the fusion of two plates. With the exception of the first or operculum, they have the antelateral angles projected forward into small lobes. In the operculum these angles are noticeably rounded away, and the anterior edge is projected into a broad median lobe. In the female the second sternite has a similar lobe. The annulate segments, or sclerites, comprising the postabdomen increase in length and decrease in breadth from the first, which is very broad and short, to the last in which the length exceeds the width of the anterior or wider end. They are depressed and have faintly defined pleural areas or flattenings at the sides. Each is prolonged on either side, at the posterior angle, into a short, striated spur, which grows longer with each succeeding segment, those on the last forming conspicuous pointed lobes. The first two segments each carry on the dorsal side four triangular scales like those of the preabdomen, the third, fourth and probably the fifth, each two, the last none. This segment has a shallow notch in the middle of the dorsal, posterior edge, marked on either side by a small denticle, succeeded toward the sides by very minute ones. The series of striations of the lobes continue up the sides of the segment to its articulation with the preceding. On the ventral portion of each ring segment is a shallow posterior emargination fringed with lobelike teeth. Extending forward from near either end is a curved rent, a pair sometimes almost inclosing an irregular, oval area.
The telson is very long, nearly equaling in length the rest of the postabdomen. For a short distance from the anterior end it contracts rapidly, then continues slender to the abruptly rounded point. The edges are sharp and, from near the anterior end, are marked by short, oblique incisions. The dorsal surface is smoothly convex, the ventral has a flat topped carina which begins near the proximal end and extends to the tip. On the carina is a double row of pits like those bordering the cephalothorax.
The doublure, at its dehiscence in the axial line, equals in width about one fourth the length of the cephalothoracic shield. From this point it narrows toward the genal angles.
The preoral appendages have not been observed. The endognathites are robust and vary greatly in length, the first pair being barely long enough to reach the shield border, while the members of the third clear it by fully three fourths their length. The fourth pair is known only by a coxal joint and a basal portion consisting of three joints. The first legs consist of seven joints; the second and third each, of eight. In the first three, each joint from the third to the penultimate is provided with two long, curved, striated spines. The terminal joints are comparatively long and clawlike. The coxal joints are large. The first three are short and broad, the length being a little less than two thirds the breadth. They have narrow, curved, postlateral prolongations equal in length to the second joint. The lower, inner angles are rounded and crenulated. The dentate faces at the inner, upper angles are on slight prolongations, which grow longer with each succeeding coxa. All three begin with two or three isolated, anteriorly directed, lobelike teeth, followed by slender conic ones, which become finer toward the posterior end. The fourth coxal joint is comparatively long. The inner lower angle is gently rounded away, and the neck supporting the narrow dentate face, long. The teeth appear to be comparatively few and coarse. The epicoxite of the third left coxa is shown on plate 16, figure 1.
The swimming arms are stout and moderately long, extending back nearly to the fifth tergite, and consist of nine joints. The gnathobases are subquadrate and large, and are provided with seven or eight short, bevel-edged denticles, the two anterior being large and prominent. The length of the gnathobase was 33 mm, its breadth 30 mm, the length of the dentate face 8 mm. The middle joints have the anterior and posterior angles sharp, in the fifth the anterior forming a blunt, striated spine, much like those at the sides of the postabdomen. The seventh and eighth joints are broadly expanded, and their margins, particularly in the latter, are marked by sparse, shallow serrations. Inserted on the inner side and near the end of the eighth joint, is a small, oval, rudimentary ninth joint.
The metastoma is elongate ovate, widest in the middle, with ends truncated. The anterior or narrower end is notched and minutely dentate.
The genital appendages of this species, so far as they are preserved in the material of the collection, are, with the exception of the part carried by the second sternite in the female, essentially like those of E. fischeri Eichw., as described by Holm. That of the female is the more complex and is carried partly by the operculum and partly by the second sternite. The part carried by the operculum follows two subtriangular areas formed by a pair of sutures extending posteriorly from either side the median lobe to meet the cleft, and extends considerably beyond the posterior edge of the plate. It consists of a short sagittate base and a slender portion divided transversely into two imbricating sections, each terminating in a short bifid expansion. In E. fischeri there is a third part consisting of two, short, flat, diverging crura. As this appears to be a general feature in Eurypterus, it is probable that it exists in this species also. The part of the appendage carried by the second sternite is covered by that of the operculum. It lies in the median cleft which extends through the posterior two thirds of the sternite, the anterior third of the two halves of this plate being fused. It is slender, being about one fourth as wide as long and does not quite reach the posterior edge of the sternite. The anterior end is slightly constricted where it fuses with the sternite, and the distal is tapering. The male appendage is confined to the operculum. In the material of the collection is a single specimen showing the exterior, the others showing the internal form only. It was evidently small, about one fifth the length of the operculum by which it is surrounded.
The body is covered with comparatively coarse, imbricating crescentic scales, most distinct on the sternites and swimming arms. When the integument of the metastoma and paired appendages are scaled away, there remains a punctate surface. The specimens found show that the size of these animals averages from 20 centimeters to 30 centimeters. A fragment of the third joint of a swimming arm was found, however, which appears to have been part of an individual over 60 centimeters in length.
In the outline, size and proportions of carapace (length : width as 2 : 3) this species resembles E. lacustris more than any other form. Moreover, the abdomen and the legs appear not to have been very different, but the telson is notably longer and more slender than in E. lacustris or in any other of our species of Eurypterus.
Before us are carapaces showing that this species grew still larger than the type specimens indicate. One of these measures 54 × 89 mm, another is 58 mm × circa 98 mm.
One of the original figures [op. cit. pl. 10, fig. 7] shows three ends of appendages with thick, clawlike terminal segments. On the left side, however, two endognathites are shown with thin spinelike terminal segments. As other specimens show that the endognathites did not possess such clawlike segments at their extremities, it is probable that Sarle's interpretation of the specimen is not correct. An inspection of the original shows that the supposed terminal segment on the middle line of the figure is one of the chelicerae, but the two others on the right hand side are oval prominences with a median sulcus but without separation of the test. We surmise, therefore, that they are the upper views of the first segments of endognathites which are displaced. A corrected figure is here given on plate 13, figure 6.
Horizon and locality. Pittsford shale, Pittsford, Monroe co., N. Y.
Eurypterus (?) (Dolichopterus?) prominens Hall
Eurypterus prominens Hall. Am. Ass'n Adv. Sci. Proc. 1884. 33: 420
Eurypterus prominens Hall & Clarke. Palaeontology of New York. 1888, 7: 157, pl. 27, fig. 3, 4
This species, the single eurypterid representative from the Clinton group, is based upon a carapace that was fully described by Hall and Clarke. These authors also point out the characters by which this species is distinctly different from any other species of Eurypterus. The most important 
Figure 38 Eurypterus? prominens Hall. Original figures. (From Hall and Clarke) of these is the anterior position of the eyes, which coupled with their submarginal position and the great length of the carapace (length to width as 27 : 30 or 9 : 10) gives the latter an aspect very like that of Dolichopterus, so that it would not be surprising if later discoveries prove this species closely allied to that genus. In Dolichopterus the specialization has gone a step farther and the carapace, which there is still well rounded at the anterior corners, has become subquadrate.
It maybe also mentioned that the youngest stage of E. remipes observed has the same long carapace and anterior eyes and that, tor this reason, E. prominens may represent a phylogenetically youthful type of Eurypterus, an inference that is supported by the geologic position of the species.
The ocelli have, as usual, followed the compound eyes and are situated well forward on a line connecting the posterior extremities of the lateral eyes. They mark the apex of the carapace. The uncompressed type specimen shows this head shield to have been relatively high, but its summit flattened and culminating in a broad ridge connecting the compound eyes.
The oblique linear depressions on the postlateral areas are rather faint and somewhat exaggerated in the drawing. Similar depressions occur in other species, as in E. maria. They appear to mark the location of a strong muscle or muscle-bearing interior process.
The specimen is supposed to have been derived from the greenish Clinton sandstones in the northern part of Cayuga county, N. Y. and is now in the collection of Cornell University.
Eurypterus pustulosus Hall
Eurypterus pustulosus Hall. Palaeontology of New York. 1859. 3: 413* pl. 83B, fig. 1
Eurypterus giganteus Pohlman. Buffalo Soc. Nat. Sci. Bul. 1883. 4: 41, pl. 2, fig. 1
Pterygotus globicaudatus Pohlman. Ibid. p. 42, pl. 2, fig. 2
Pterygotus globicaudatus Laurie. Roy. Soc. Edinburgh Trans. 1893. v. 37, pt 2, p. 515
Hall based his species upon a single fragmentary and rather poorly preserved carapace, now in the American Museum of Natural History. This, however, is fully 
Figure 39 Copy of original figure of Eurypterus giganteus Pohlman. (From Pohlman) competent to show the most characteristic features; the form of the carapace, the position of the lateral eyes and peculiar ornamentation.
More than a score of years later, Pohlman found in the Museum of the Buffalo Society Of Natural Sciences another much better preserved carapace [here reproduced in pl. 23, fig. 1] and he recklessly denoted it as E. giganteus, stating that his species had markings like those of E. pustulosus but that "the shape of the carapace and the position of the eyes are so totally different that the two species can be distinguished very readily." As a matter of fact, the proportions of the carapace and the positions of the eyes are quite the same in both specimens [see under Measurements].
Figure 40 Copy of original figure of Pterygotus globicaudatus Pohlman. (From Pohlman)
In the same publication Pohlman added several "new species" of Pterygotus to those before described from the Buffalo waterlimes by Grote & Pitt, increasing the number to a half dozen, all of which are synonyms of P. buffaloensis save one. This latter was described by Pohlman as P. globicaudatus. It is based on a single postabdomen, in relief and counterpart, now in the Museum of the Buffalo Society. The two were combined in one figure, here copied [text fig. 40]. This figure illustrates the three principal characters of the specimen, viz, the bladelike extensions of the postlateral angles of the segments, the apparent globosity of the "telson" which gave the species its name and the coarsely pustulate sculpturing.
This "telson" [pl. 24, fig. 1] has, at first glance, the features ascribed to it by Pohlman. It appears to have a round outline; the upper and lower plates have separated and a thick mass of matrix lies between them, suggesting the globose character attributed to it. But such a "telson" would have compelled this unfortunate creature to drag, like a member of an old-time chain gang, a cannon ball after him all his life. This structure
 Figure 41 Counterpart of original of Pterygotus globicaudatus Pohlman. Natural size |
The telson of globicaudatus is hence unknown and the term undoubtedly a misnomer.
The postlateral extensions of the segments are faintly indicated in Pterygotus anglicus but absent in other members of that genus. Some species of Eurypterus, however, as E. pittsfordensis, have them equally well developed and they also appear to represent an ontogenetic feature of the young of other members of this genus.
The third peculiar character of this species is the "scales." They differ indeed from the surface sculpture of most eurypterids and consist of relatively large [1 mm], circular disks, many of which are flat-topped while in most the center is slightly sunken or the margin raised. Under enlargement [pl. 24, fig. 4] most of the scales have the anterior margin less rounded and in many the disk is distinctly heart-shaped. About the center are two darker spots which represent a pair of pitlike depressions. The scales are largest and most crowded on the anterior half of the segment. The overlapped anterior fifth of the segment is sharply set off from the remainder by a line of oval disklike scars and the overlapped part itself is densely crowded with smaller scales which in front consist of crescents and behind change gradually into the disks, thereby evincing the morphologic and functional identity of these peculiar disklike scales with the crescentic scale of other eurypterids.
A brief study of the ornamentation of Pohlman's type of E. giganteus ( = E. pustulosus Hall) figured on the same plate as his Pterygotus globicaudatus, shows it to be of quite the same character and relative dimensions as the latter, the fact being taken into account that the sculpture pustules of the eurypterids are always of smaller size and at the same time more prominent on the carapace than on the body. The enlargements of the ornamentation of the type of E. giganteus [pl. 24, fig. 2, 3] show that the carapace was covered with large wartlike pustules in front of the eyes, which are flat on top or slightly sunken in. They are now filled with rock and were hence originally hollow and probably rounded on top. Between them are found many smaller ones, scalelike, with thicker test, which exhibit the disk shape of those of P. globicaudatus, as seen on the anterior portions of the segments [pl. 24, fig. 4]. Like scales are observed on the first tergite of the type of E. giganteus and since the sculpturing as a rule increases in coarseness from the first tergites posteriorly, there is no doubt that this ornamentation fully corresponds to that seen on the postabdomen of P. globicaudatus.
It is hence, manifest that P. globicaudatus and E. giganteus are of the same species and as E. giganteus is identical with E. pustulosus the original P. globicaudatus represents the postabdomen of E. pustulosus. The species characters are then the following:
Description. Body medium-sized to large. Carapace semicircular, nearly twice as wide at base as long (length : width as 6 : 11), probably originally quite high (as indicated by concentric wrinkles); lateral and frontal margins forming a continuous circular curve, when the carapace is flattened; the thickened edge scalloped; posterior margin straight and transverse, genal angles nearly rectangular; compound eyes relatively small (one seventh the length of carapace), consisting of a bean-shaped, very prominent ocular node and narrow reniform visual surface, situated halfway between the frontal and basal margins, far apart (three fourths as far from lateral margin as apart); the ocellar node prominent, in exact middle of carapace.
First tergite one fifth as long as the carapace, nine times as wide as long. Postlateral angles truncate. Postabdomen at its anterior end about three fourths as wide as long and tapering to about one third of its anterior width. The segments possess distinct epimera which become increasingly winglike posteriorly, on the last segments possessing sigmoidal margins.
Ornamentation. The ornamentation of the carapace and postabdominal segments has been described above. From an exfoliated portion of one specimen [pl. 23, fig. 1] it is seen that the test of the marginal shield of the cephalothorax was furnished with wartlike, round pustules.
Measurements. Carapace of type, 67 × 120 mm (as 6 : 10.7); that of Pohlman's type of E. giganteus 50 × 93 mm (as 6 : 11). Eyes in type 41 mm apart and 30 mm from lateral margin; in other specimen 7 mm long, 31 mm apart and 24 mm from margins. First tergite of this specimen 9.5 mm long. Postabdomen about 150 mm wide at anterior end, 210 mm long and about 50 mm at posterior end.
Horizon and locality. Bertie waterlime at Buffalo.
Remarks. A third carapace (with attached first tergite) of like dimensions with the type of the species is in the Buffalo Museum. It is noteworthy for the distinctness of the ornamentation of the first tergite, consisting of a narrow anterior zone of very closely arranged tubercles and the characteristic disklike scales which here are larger, more numerous, and more prominent than in the other two specimens. This specimen also demonstrates that the scalloping of the edge of the carapace is due to the presence of scales.
The National Museum contains a fragment [pl. 23, fig. 2] of a very large carapace of this species from the waterlime at Buffalo which indicates that the species must have attained much larger proportions than any other known Eurypterus. This carapace was approximately 250 mm wide in front of the eyes, to which a basal width of about 300 mm and a length of the carapace of about 160 mm would correspond. The whole body must have measured fully one meter.
There is no species of Eurypterus which this form closely resembles, and it must represent an aberrant branch of the genus, if, indeed, it actually belongs in the genus at all. Only the carapace and the postabdomen of the animal are known and the appendages may prove to be quite different from those of Eurypterus. In this connection it is suggestive that the Scottish representatives of Laurie's genus Drepanopterus possess some of the features in which E. pustulosus differs from typical Eurypterus [Laurie. 1892, pl. 3, fig. 16; 1899, pl. 3, fig. 17; pl. 4, fig. 22]. Drepanopterus pentlandicus exhibits strong "granular markings" which, judging from his figure [pl. 4, fig. 22], may well resemble those of E. pustulosus in size and distribution, while in D. lobatus the posterior angles of the postabdominal segments are produced into like processes. On the other hand, E. pustulosus does not possess the characteristic form of the carapace of the Drepanopterus-Stylonurus group and in the lobation of the postabdominal segments and its strong ornamentation, it suggests the last Carbonic representatives of the race, notably E. mansfieldi Hall and E. (Anthraconectes) mazonensis.
Eurypterus pristinus nov.
Description. Carapace broadly subrectangular, about one half longer than wide (width, 20.5 mm, length, 13.5 mm). Anterior margin slightly convex, antelateral angles well rounded, lateral margins nearly parallel, slightly concave in the middle and curving outward toward the genal angles which are slightly produced sideways; posterior margin nearly straight transversely; eye nodes subcircular, small (about one seventh the length of the carapace), situated just forward of the center and twice their diameter from the lateral margin; the form and size of the visual surface have not been made out.
The surface of the type specimen exhibits, especially on the posterior portion, low, rather broad nodes, so closely arranged as to be in contact at their bases. A body segment lying close to the carapace possesses a similar ornamentation.
Patches of integument are found associated with the eurypterids at Schenectady which present the aspect of a shagreen, their surface being covered with low, flat nodes which in many places become so crowded that they assume polygonal outlines. We consider it probable that these patches belong to this species.
Horizon and locality. Frankfort shale. Dettbarn quarry, Schenectady, N. Y.
Eurypterus ranilarva nov.
Description. Body of small size, very plump in general appearance, the carapace and preabdomen forming a broad oval from which the postabdomen is set off rather abruptly.
The carapace is strikingly broad (length : width as 5 : 7) and nearly as wide as the broad preabdomen; subrectangular in outline; anterior margin straight to slightly emarginate in the middle and rounded at the anterior corners; lateral margins gently convex, slightly contracted toward the posterior angles; its doublure remarkably broad, forming a wide rim (4 mm) that gradually narrows along the sides; it bears a deep broad furrow in the middle that ends somewhat abruptly just behind the anterior corner, and fine parallel striae on the flat portion outside of the furrow; along the inner edge of the furrow runs a narrow crest. The rim seems to have been produced into a relatively large triangle in the middle line. The eyes were large (between one third and one fourth the length of the carapace), reniform in outline and situated on the anterior half of the carapace, separated by about their own length from the outer margin. The preabdomen is so broad that its length is to its width almost as 2 : 3. The broadest part is in the region of the fourth tergite or third sternite. On account of the complete flattening of the specimens, both the tergites and sternites appear only as ill defined bands, the overlap, and consequently the true length, of which can not be determined. So much, however, is certain that they were rather short and wide, about seven times as wide as long. Their doublures can not be satisfactorily seen. The postabdominal segments are better shown and their broad posterior doublures well observed in all specimens. The postabdomen is relatively short and broad, it reaches not more than one third the length of the body while in the typical species of Eurypterus it amounts to one half of that length. It tapers gradually to not quite one third its anterior width. The postabdominal segments are short, the length of the penultimate segment to its width having the proportion of 2 : 3. The ultimate postabdominal segment is furnished with two short blunt lobes of the postlateral angles. The telson, corresponding to the rest of the body, is short and strong, rapidly tapering to the distal extremity. Its length was apparently only about one fourth or one fifth of the whole body.
Appendages. The limbs indicate that this species was a better walker than swimmer, for while the walking legs were strong and well developed, the swimming legs are rather slender and furnished with but small paddles. These paddles also seem to have ended in a spine although the evidence on this point is not conclusive, only a single indication of the spine having been seen. The details of the walking legs are not very distinct. The last pair, which typically in Eurypterus is comparatively slender, is here short when compared to the great width of the carapace, but somewhat broad jointed. The swimming legs are long in comparison with the short body. When turned back they reach to the posterior edge of the preabdomen. The coxae of the swimming legs are apparently large, occupying in length one half that of the carapace and of the usual trapezoidal outline. The following segments of the swimming legs are short and stout but not as short as in the typical forms. Likewise the next two segments (nos. 4 and 5) are long and tubular like those of the walking legs. The sixth segment is shorter, and the seventh and eighth are broadened to about double the width of the other segments to form the paddle. They were of subequal size; the eighth segment formed a broad oval approaching a circle.
The metastoma appears to have been broadly elliptic (length to width as 3 : 2), not half as long as the carapace.
The genital appendages have been seen only as faint shadows, too indistinct to describe.
The ornamentation of the surface is also obscured to such an extent by secondary roughening and wrinkling of the integument that nothing reliable can be ascertained.
Measurements. The largest specimen (no. 12905, University of Chicago collection) measures 160.5 mm in length and 53.5 mm in greatest width. Its carapace measures 35 × 49 mm. The rim is 4 mm wide, the eyes are 10 mm long, the metastoma 14.5 mm. The swimming leg projects 41 mm beyond the margin of the carapace. The preabdomen is 40 mm long and 53.5 mm wide; the postabdomen is 50 mm long, 43 mm wide at its proximal end and 14 mm at its distal extremity. The telson measures 35+ mm. In another well preserved specimen (no. 12907, University of Chicago collection), which is 154+ mm long, the dimensions of the carapace are 33 × 48 mm; those of the preabdomen 43.5 × 52.5 mm, of the postabdomen 41.5 mm, of the telson 36+ mm.
Horizon and locality. Kokomo waterlime, Kokomo, Indiana.
Remarks. This is probably the species cited by Claypole [1890, p. 259] as E. lacustris from Kokomo, for in its broad carapace it is most likely to suggest that form. It resembles still more, however, the E. dekayi of the Buffalo waterlime, which is built on like proportions, possessing a similar broad carapace and preabdomen and a still shorter postabdomen. The slender swimming legs of ranilarva serve at once to distinguish it from this Buffalo species. Its nearest relative is obviously the E. kokomoensis of the same locality with which it has many characters in common, notably the broad plump form of the body, the broad doublure and the weak development of the swimming legs. Its principal distinguishing character from the latter is the greater width of the carapace, as a comparison of figure 7, plate 17, and figure 1 on plate 25 will readily show. In E. kokomoensis the width surpasses the length by one fifth and in E. ranilarva by one third. It is possible that these differences are only those of sex, a point that at present can not be determined since the opercular appendages of E. ranilarva are not distinctly shown.
A younger specimen (no. 12906, University of Chicago collection) [pl. 18, fig. 2] is interesting in showing a relatively broader carapace and preabdomen, a shorter body, and more abrupt contraction to the postabdomen, which is much more slender than the rest of the body. It thus displays distinctly immature features, corresponding well to those observed in other eurypterids.
Eurypterus? (Dolichopterus?) stellatus nov.
Description. Carapace subtrapezoidal, width (22 mm) a little less than twice the length (13.5 mm). Posterior margin slightly arched forward in the middle third, lateral margins curved, flatly sigmoidal, slightlv converging forward; frontal margin not clearly seen, but apparently gently convex.
The compound eye is elongate elliptical in outline, very large, one third of the length of the carapace (4 mm in type specimen), situated near the antelateral angle; the visual surface is long and curves far inward at both ends. The ocelli seem to be situated behind the center of the carapace.
The ornamentation of the carapace consists of sharply elevated, hollow tubercles, densely arranged and evenly distributed (absent, however, on the eye nodes) and frequently with a stellate form or provided with a few radiating ridges or wrinkles. A fine granulation occupies the interspaces between the tubercles.
Horizon and locality. Frankfort shale (Schenectady facies) in Dettbarn quarry at Schenectady, N. Y.
Remarks. The forward position and form of the eyes suggest that the species may belong to Dolichopterus, but the carapace is markedly shorter than that of other members of the genus.
Besides the carapace a number of patches of integument have been found which still better display the peculiar stellate ornamentation and the finer granules.
Subgenus ONYCHOPTERUS nov.
This subgenus is proposed for Eurypterus kokomoensis to give expression to the phylogenetic importance of the species as indicating the path of development of Dolichopterus, Drepanopterus and Stylonurus from Eurypterus. Its distinctive characters are the large, squarish carapace, the lack of differentiation of the fourth pair of endognathites, the spurlike form of the ninth segment of the swimming legs and the styliform telson.
Eurypterus (Onychopterus) kokomoensis Miller & Gurley
Eurypterus kokomoensis Miller & Gurley. Illinois State Mus. Bul. 10. 1896. p. 90, pl. 5, fig. 1
Description. Body of small size, relatively broad, about three and a half times as long as wide, attaining its greatest width in the region of the fourth tergite, thence tapering gradually to the telson.
The carapace is decidedly squarish in outline, its anterior angles are rounded and it is little wider than long. The anterior margin is slightly convex and emarginate, the lateral margins subparallel and nearly straight. The lateral eyes are apparently reniform and not very large, about one fourth to one fifth the length of the head shield. They lie on the anterior half of the carapace, just in front of the bisecting transverse line. The ocelli have not been seen. The doublure of the carapace is very broad in front, about one ninth the length of the head, narrowing somewhat posteriorly, distinctly produced in the median line to form a small triangular shield.
The abdomen is little wider than the carapace, the preabdomen as wide as long, and the postabdomen relatively short and compact, longer by one third than the preabdomen. The tergites are short, the length about one sixth of the width, with broadly concave posterior margins in the middle half. The sternites are longer (length : width as 1 : 4.5), the operculum apparently but little different from the other sternites in size and outline. In compressed specimens their anterior margins are almost straight. The doublure is apparently narrow. The posterior margins are deeply concave in the middle portion and project into broad, rounded lobes at the lateral angles. The doublure widens under these lobes so that its anterior margin is approximately transverse. All sternites bear transverse oval gill plates whose major diameter is twice the minor. Those of the operculum are but half the size of the others and those on the last pair of sternites are smaller. The postabdominal segments gradually increase in length posteriorly, the last being twice as long as the first, but only one third as wide. The posterior doublure is narrow (1.5 mm). The last segment is produced at the postlateral angles into two short broad lobes with blunt extremities. The telson is short and thick, a little more than one fifth the length of the body. It contracts very rapidly in its first third, then more gradually to its blunt extremity.
Appendages. Only four pairs of limbs have been observed, viz, the three last pairs of walking legs and the swimming legs. The walking legs, notably the last pair, are relatively a little stronger than those of most other members of the genus, while the swimming legs are slender and bear a long terminal spine in place of the "claw," thereby indicating their primitive condition as natatory organs and their functional adaptation to walking organs. The coxae of the swimming legs are distinctly seen in the type specimen. They are relatively small, considerably less than one half the length of the carapace, long at their inner margin and subrhomboidal in general outline, the anterior and posterior margins being rather oblique and long. The fourth, fifth and sixth segments are longer than in the later species of Eurypterus and distinctly tubular, while the seventh and eighth are not nearly of the relative size and width in E. remipes or E. fischeri. Both are about equal in length, not longer than the preceding ones. The seventh segment is as wide as long and the eighth subcircular. The terminal spine is more than half as long as the preceding segment, slightly curved. The metastoma is small, measuring little more than one third the length of the carapace, oval in form; the anterior portion slightly narrower than the posterior one.
The genital appendages have been clearly seen in only one specimen, a female [pl. 26, fig. 2]. They are here so long that they reach to the posterior margin of the third sternite. The paired basal plates are visible only in faint outline. They were apparently of the usual shape. The first median lobe distinctly spreads in posterior direction and its paired extremities are produced into relatively long laterally curved alae that extend to the posterior margin of the second sternite. The second median lobe is but little shorter than the first and of less, though uniform, width. The terminal paired appendages are long (as long as the second median lobe) and slender, slightly curved outward.
Ornamentation. The type specimen shows on the last postabdominal segments where patches of the surface are preserved, very small, evenly distributed, sharply angular or pointed scales.
Measurements. The type specimen is 136 mm long. Its carapace measures 28 mm in length and 34.7 mm in width; the preabdomen is 32.3 mm long and 39.4 mm wide; the postabdomen 42.2 mm long, 31 mm wide at its beginning and 12.5 mm at its posterior end. The telson is 30.4 mm. The metastoma is 9.5 mm long, the swimming legs are about 52 mm long each. Judging from the size of the genital appendages (in specimen 12909 University of Chicago) all specimens before us are of mature age and the species probably did not reach a much larger size than that exhibited by the largest specimen before us. This attained a length of 125 mm to the base of the telson (which is but partly preserved), to which may be added at least 34 mm for the telson, giving a total length of 159+ mm, to which corresponds a greatest width of 50.5 mm, a figure clearly exaggerated by the strong flattening of the specimen. The carapace measures 33.7 × 40 mm. The eyes were about 7.6 mm long and the amount of their length distant from the margin. The limbs appear very small in this specimen; the swimming legs extending but 44 mm beyond the lateral margin of the carapace.
Horizon and locality. Noblesville waterlime at Kokomo, Indiana.
Remarks. The material before us consists of four specimens, three from the museum of Chicago University, among these the type, and one from the collections of the State Museum. The type specimen is exceptionally preserved for Kokomo eurypterids. It exhibits all details of structure but the original figure does not do it justice as the specimen had not then been worked out nor the extremities of the limbs, among them the curious spines of the paddles, exposed. For these reasons this specimen has been refigured [pl. 25, fig. 1] and a drawing added of one of the other specimens [pl. 25, fig. 2] which shows the faint outlines of the eyes, and is remarkable for its size and exhibits well the terminal spines of the paddles. The third specimen is entirely unique in its preservation [pl. 26, fig. 2]. As shown in the reproduction, the gill plates are preserved as thick, black, roughly surfaced blotches, while the whole specimen appears as hardly more than a color stain. We have more fully referred to this specimen in the general remarks on Eurypterus. The doublures of the segments also come out with remarkable distinctness as dark bands and the female opercular appendage is distinctly set off from the darker background. The sutures of the basal plates of this appendage are barely discernible.
The fourth specimen is very fragmentary, poorly preserved and recognizable as belonging here only by the presence of the terminal spines of the paddles.
E. kokomoensis bears some similarity to E. remipes in the squarish outline of its carapace and the proportions of the carapaces and preabdomina. It was not so well adapted to swimming as is shown by the less developed and more slender swimming legs and the presence of a terminal spine, obviously used in walking, and also by the shorter and stouter postabdomen. While the species may have been a less active swimmer, the extremely broad doublure of the carapace may indicate an adaptation of the front edge to shoveling or digging.
Subgenus TYLOPTERUS[7] nov.
This subgenus is proposed for the species, Eurypterus boylei, described by Whiteaves from the Guelph formation of Ontario; a form which exhibits a number of characters that show it to be an aberrant type distinctly adapted to the peculiar conditions of the Guelph sea. These special traits are found in the thick integument of carapace and abdomen which apparently was not only chitinous but calcareo-chitinous; the highly raised lateral margins of the carapace and the presence of elevated and divided knots on the second to fifth tergites.
The extraordinary thickness of the test is shown not alone in the wholly uncompressed condition of the carapace but more in the fact that, though the abdomen has been shoved forward so that the segments are pushed into each other like joints of a telescope, they have not suffered from crumbling or folding as they always do in the other eurypterids and their greatly thickened posterior edges stand out freely. The front margin of the carapace forms a broad beveled shoveling edge, while the lateral margins are much thickened and elevated into prominent ridges. The abdomen seems to have been very compact and short, as shown by the relatively short last two postabdominal segments. The telson spine is also short and thick. The surface of the carapace exhibits in front an unusual sculpture consisting of intricately mingled short, coarse, curved ridges of confluent tubercles. On the posterior part of the carapace the tubercles are mostly separated. The axial knots on the segments were solid bodies. All these features combined demonstrate that the integument of this subgenus was not merely chitinous as in the typical Eurypterus, but much strengthened by calcareous deposits which became most prominent in the sculpture of the carapace and in the knots of the tergites.
Figure 43 Tylopterus boylei (Whiteaves). Holotype refigured in natural size, and enlargement of sculpture of carapace
This thickening of the carapace is entirely in accord with the character of the Guelph fauna described by the authors from New York, where the fact of the peculiar thickening of the shells in all classes, notably the brachiopods and mollusks, has been emphasized and been ascribed to the strongly saline water and in part to the life of the organisms on wave-beaten coral reefs. Tylopterus boylei seems to be an adaptation to the same peculiar conditions which are also indicated by the character of the matrix of the fossil, a porous, coarse-grained dolomite.
It would suggest itself to compare this species with the Carbonic eurypterids described by Etheridge (E.? stevensoni, see text fig. 48) and Woodward (E. scabrosus) in which the integument has become greatly thickened by deposition of globular calcite ("calculi"). We have in another place considered these features as phylogerontic in the Carbonic subgenus Anthraconectes and as due to the waning vitality of the race. It is hardly to be assumed that the characters of the Siluric T. boylei are due to the same gerontic conditions and that the latter is an ancestor of the Carbonic Anthraconectes. It would for this reason be unwarranted to unite it with the latter subgenus, especially since both lived under unlike abnormal marine conditions, that is, Tylopterus in very saline water, Anthraconectes in brackish or fresh water.
Tylopterus boylei (Whiteaves)
Eurypterus boylei Whiteaves. Paleozoic Fossils, v. 3, pt 1. 1884. p. 42. pl. 7. fig. 3
The species was very carefully described by Whiteaves as follows:
Carapace moderately convex, broader than long, greatest breadth a little above the middle; semiovate, broadly rounded in front and squarely truncated behind; sides somewhat convex at their margin above, but straighter below; front and sides bordered by an elevated, narrow ridge, which is highest and most strongly marked on the posterior half of the sides. Eyes reniform, prominent, about 4 mm in the greatest diameter; 9 mm apart (as measured from the center of their inner margins) and placed at a distance of 6 mm from the anterior, and of 7 mm from the lateral margin. Ocelli not clearly indicated, but probably placed on or near a small rounded prominence or elevation, which is situated exactly in the middle of the space between the two eyes. Surface of the carapace apparently finely granulose, and ornamented with minute rounded tubercles, some of which are isolated and others confluent in sets of two or three.
Thoracic and caudal portions together consisting of 12 segments, exclusive of the telson or caudal spine; the first, second, third and fourth thoracic segment each bearing on the median line a single, large and prominent, transversely elongated tubercle, which is arcuate or reniform at its base and somewhat bilobate at its summit. The lateral diameter of each of these tubercles greatly exceeds the longitudinal, and measuring at their base, the proportions of each tubercle may be thus approximately estimated; that on the first thoracic segment, lat. diam. 4 mm, long diam. not quite 1 mm; that on the third, lat. diam. nearly 5 mm, long diam. rather more than 1 mm; that on the third, lat. diam. 5 mm, long. diam., 2 mm; and that on the fourth, lat. diam. 5½ mm, long diam., 3 mm.
Telson produced into a gradually narrowing, slightly curved, and rather obtusely pointed linear spine, which seems to be triangular in transverse section.
Antennae, endognaths and ectognaths unknown, as is also the nature of the surface markings of the test of the thoracic and caudal segments.
Entire length, including the telson, about 75 mm (or 3 in.); length of carapace, 20 mm, greatest breadth of the same, 27 mm; length of telson, 15 mm.
Tylopterus boylei is known in only a single specimen preserved as a mold of the dorsal surface. Guttapercha squeezes of this show that the knots are not located on the first to fourth segments as stated in the original description but on the second to fifth. The squeezes also show distinctly the ocelli on the prominence between the lateral eyes. On the right side also two segments of the fourth ectognathite (balancing leg) are seen and on the opposite side the edges of two flat segments, apparently the oar plate of the swimming leg. The legs seem, therefore, to have agreed with those of Eurypterus.
Subgenus ANTHRACONECTES Meek & Worthen[8]
Meek and Worthen suspected that their species Eurypterus mazonensis from the Lower Coal Measures (Pennsylvanian) represented a distinct subgenus, if not a genus, for which they proposed the name Anthraconectes. They state that this fossil "differs from the typical forms of Eurypterus particularly in the great length and single extremity of the mesial appendage of its operculum, as well as in the possession of two little spatulate supplementary pieces." Hence they "strongly suspect that other characters will be found, when better specimens can be studied, showing it to belong to a distinct subgenus, if not indeed to an entirely distinct genus from Eurypterus proper."
Hall suggested that these differences may not be of great importance [op. cit. p. 26] and emphasized the fact that the species from the Pennsylvania Carbonic are typical Eurypteri [p. 27].
While we agree with Meek and Worthen that the peculiar character, of the opercular appendage would warrant a separation of the species from typical Eurypterus, we believe that the preservation of this organ is not so distinct that its characters are beyond doubt. On the other hand, we have no doubt that Anthraconectes mazonensis has a number of characters in common with the Pennsylvania and also with British Carbonic species which distinctly indicate a phylogerontic condition
 Figures 43–47 Eurypterus (Anthraconectes) mansfieldi C. E. Hall. Figure 43, a small, fairly perfect specimen, ×3; figure 44, large specimen, natural size, showing the long epimera; figure 45, a nearly entire small individual, showing the extremely slender telson and the doublures of the postabdominal segments; figure 46, the fourth endognathite, ×2; figure 47, enlargement of test with narrow, triangular scales. (From James Hall) |
Figure 48 Eurypterus (?) stevensoni Etheridge. Spines and scales. (From Etheridge) margins of the abdominal somites is also present in British Carbonic forms, as is amply evidenced by E. scouleri Woodward[12] with its long pointed scales, E. (?) stevensoni R. Etheridge jr [Geol. Soc. Lond. Quar. Jour. 1877. 33:223] in which the surface is covered with long blunt spines and scales, giving it the appearance of a mass of congealed drops, while in E. scabrosus H. Woodward[13] the scales have become prominent wartlike tubercles, interspersed with disklike bodies which proved to be "calculi" or bodies of globular calcite formed inside the integument. All these excrescences are distinctly phylogerontic and seem to indicate that the eurypterids which in the Upper Siluric were the lords of the sea, were now put largely on the defensive. Fritsch has contended [1904, p. 77] that Glyptoscorpius is but an eurypterid and that the supposed combs are merely long fringes at the posterior margins of abdominal segments, and if this is correct then this genus may represent an extreme development of Anthraconectes.
The third feature which the Carbonic species have in common is the exaggeration of the development of the epimeral pieces of the abdominal segments, well seen in the figure of E. mazonensis on the left side [text fig. 50]. E. mansfieldi shows the same features very clearly 
Figure 49 Eurypterus approximatus Hall & Clarke. Copy of original figure [text fig. 44] and E. approximatus possessed long and recurving epimera on the preabdominal segments (the postabdominal segments are not satisfactorily preserved in the single type). These epimeral pieces are produced into strong recurving spines [text fig. 49] and the character is hence entirely in line with the spinosity of the surface, increasing the gerontic aspect of these species.
Another important distinctive character is the lack of differentiation between the first three pairs of endognathites and the last pair. This is especially distinct in E. mansfieldi [text fig. 43]. Finally these species of Anthraconectes were fresh or brackish-water animals while the true Eurypteri were marine.
Even if the characters of the opercular appendage noted by Meek and Worthen should not warrant the recognition of this subgenus, the features mentioned which are common to the majority of the Carbonic Eurypteri are fully competent to verify their suspicion that "other characters will be found showing it to belong to a distinct subgenus—if not indeed to an entirely distinct genus from Eurypterus proper." It is on the sum of these characters that we would base the subgenus Anthraconectes.
Eurypterus (Anthraconectes) mazonensis Meek & Worthen
Eurypterus (Anthraconectes) mazonensis Meek & Worthen. Am. Jour. Sci. & Arts. 1868. 46: 21, figure
Eurypterus (Anthraconectes) mazonensis Meek & Worthen. Geol. Sur. Illinois. 1868. 3: 544, figure
Eurypterus (Anthraconectes) mazonensis Hall. Pennsylvania 2d Geol. Sur. Rep't of Progress, PPP. 1884. p. 25, fig. 2, 3
Meek and Worthen have elaborately described and illustrated by an outline sketch this species from the iron stone concretions of the Carbonic of Mazon creek, Illinois. Their material consisted of but one specimen which exhibits the ventral side. Professor Whitfield kindly pointed out to us that the counterpart of this type is in the American Museum of Natural History and this has been made accessible for our study. The latter is a well preserved intaglio which happily complements the type. We therefore embrace this opportunity to add such data to the knowledge of this curious species as are furnished by this specimen. The most remarkable of these is the strong contraction of the postabdomen.
The excellent photograph[14] reproduced on plate 26, figure 1 shows the condition of the specimen and all essential features observable in it. Some structures, as the position of the eyes, the outline of the impression of the opercular appendage, are only observable with favorable illumination. It has been possible to demonstrate the outlines of the carapace and first tergites a little better than shown in the photograph. These features as well as the outlines of the doublures of the tergites are illustrated by a text figure. For the sake of completeness we have also copied the outline drawing of the ventral side, given by Meek and Worthen.
Description. Body long, elliptical in outline, with the posterior third truncated by the abrupt contraction of the postabdomen. It is widest in the region of the fourth tergite, increasing gradually from the front of the head shield to that segment and then decreasing as gradually to the second postabdominal segment where a contraction to half the width takes place.
The carapace appears to have been subrectangular, rather short and broad; length to width in the approximate proportion of 3 : 5. The lateral
 Figures 50, 51 Eurypterus (Anthraconectes) mazonensis Meek & Worthen. Figure 50, copy of original figure; figure 51, outline sketch of counterpart of original, slightly reduced [see pl. 26, fig. 1] |
margins are slightly convergent, at least in the middle portion where they can be traced. The antelateral angles are somewhat abruptly rounded, the frontal margin transverse, slightly emarginate in the middle. At the postlateral angles the carapace is a little more broadened. The posterior margin is overlapped by the first tergite and not exposed. The eyes are seen as rather small and slight kidney-shaped depressions; the right eye in the specimen is distinctly outlined by its chitinous section. Their length is but one sixth that of the carapace. They lie a little in front of the middle of the carapace and about four times their width from the lateral margin.
The preabdomen is the broadest part of the body, broader by one fourth than it is long. Its sides are subparallel, as it increases but little in breadth to the fourth tergite, and then decreases again. The lateral margins of each tergite converge anteriorly so that the postlateral angles project along the sides. The first tergite is only half as long as the others. Its lateral portions are produced forward into flat lobes, as they are also in the next tergite, while in the following two the anterior margins are nearly straight and in the last two they are gently convex forward. The first tergite is entirely flat and smooth, the following are slightly raised in the middle portions of the posterior belt and culminate in a round median node highest on the third tergite and obscure on the last.
Of the postabdomen three segments and a portion of the fourth are shown. The first is of similar width and shape as the last tergite but furnished with long, striated spines at the postlateral angles, as are also the following postabdominal segments. The second segment is but half as wide as the first, but longer by one third. Its epimera are drawn out into long, slightly curved, oblique, posteriorly directed spurs. The last segment fully exposed is again longer and carries a still longer spur on the side.
The third postoral appendage is preserved nearly entire. It was short and stout. Impressions of spines appear on one of the segments. Of the fourth limb five slender segments are shown, so that this is probably also entire. Of the last limb, the five short basal segments, following the coxa are exposed. The other side also retained portions of the last two segments which were long and formed a paddle as in Eurypterus and Pterygotus. The specimen also retains the second limb which is a short stout walking leg ending in a spine.
The impressions of the coxae of the swimming legs, figured by Meek and Worthen, are also faintly seen in this specimen. So also are impressions of the opercular appendage; especially distinct is that of the anterior hastate part.
The ornamentation of the dorsal side is very striking. The carapace is for the most part smooth, but on the middle posterior region there appear small prominent tubercles most of which are semilunar and project backward. They are irregularly crowded around a median smooth depression. Along the posterior margin the semilunar scales are abruptly changed into two rows of larger, sharply angular scales. The first tergite is smooth; the following tergites as well as the postabdominal segments show a dense mass of extremely small semilunar to linear scales on the anterior half (mostly of so small size that these parts appear smooth), while the middle posterior halves bear prominent angular scales that are largest upon the median nodes. Toward the sides the angles of the scales become smaller until linear scars are formed, making a system of parallel oblique lines on the epimera (not well shown in the figures).
Measurements. The carapace is 32 mm long and approximately 53 mm wide at the base. The eyes were 5.5 mm long and 16 mm apart. The preabdomen measures 46 × 62.5+ mm. The first tergite is 4 mm long; the second 7.5 mm long and 59 mm wide; the third is 9.5 mm long and 61+ mm wide. The first postabdominal segment measures 9 × 52 mm, the next 11.5 × 26+ mm. The limbs are only fragmentary.
Horizon and locality. Lower Coal Measures of Mazon Creek, Grundy co., Illinois. Counterpart in American Museum of Natural History (no. 8532).
Genus EUSARCUS Grote & Pitt
The most striking and interesting eurypterid of the waterlimes of Buffalo is undoubtedly a large animal which, when discovered in 1875, was made the type of a new genus and species by Grote and Pitt under the designation of Eusarcus scorpionis. The authors of the genus gave no generic diagnosis but the following description of the species suggests what they considered as its distinctive characters:
The cephalothoracic portion appears to be separate from the body, and to be considerably narrower in proportion than in allied forms. The legs are in the same number as in Eurypterus. The swimming feet appear to differ by the straighter, less rounded outer margins. In the specimen the rhomboidal plates are not given. From the impressions of the joints of the swimming feet their relative dimension does not seem to accord with Eurypterus. The four pair of anterior feet proceed from two elongate oral plates of which the impression is very distinct. The spines of the anterior feet appear to be long, curved, and to have an anterior direction. The absence of chelate appendages to the posterior margin of the feet is particularly noticeable. The first seven broad segments of the abdomen form a large ellipse. There is an evident and remarkable narrowing of the succeeding caudal segments. Of these six appear to be made out on the specimen. The surface of the cast is punctate with scattered triangular impressions. The cast shows a widening of the terminal segment and no traces of a spiniform process are exhibited.[15]
Of the differentials indicated in the passage quoted, the following have stood the test of larger collections: the much "narrower" cephalothoracic portion, the broad large ellipse of the abdomen and the "remarkable narrowing" of the postabdomen ("caudal segments"). At least three, possibly four species, exhibiting quite similar characters of general form, are known from the British Siluric rocks and these have been referred to Eurypterus by Woodward, the differences in outline not being considered of generic importance by that eminent authority. It is not surprising therefore that authors generally have shown little inclination to recognize this genus Eusarcus.
Grote's successor as curator of the Buffalo Society's museum, Mr Pohlman, was apparently the first to assail the proposed genus, stating [1886, p. 29] that the discovery of several new specimens had shown that the form has "the leading characteristics of the genus [Eurypterus], as given by DeKay," viz, "a terminal joint prolonged into a sublinear or lanceolate triangular spine with serrated edges," and "eyes reniform or oval, placed within the margin of the carapace." Pohlman's observations in regard to the telson, which is as in Eurypterus, are correct, but the original of the supposed carapace of Eusarcus which he figures [op. cit. pl. 3, fig. 3] and which is now in the collection of Columbia University, proves to be a carapace of Dolichopterus siluriceps [pl. 26, fig. 3], in which the eyes are normally intramarginal. We have however specimens of Eusarcus scorpionis which leave no doubt of the marginal position of the eyes in that species, and thus afford an important differential of the genus. In none of the British species with typically Eusarcuslike outlines (viz, Eurypterus scorpioides and E. punctatus) was the position of the eyes known to Woodward, and one species, of which only the triangular carapace and subcircular abdomen have been found, was referred by him to Pterygotus (P. raniceps) on the strength of its marginal eyes.
Grote and Pitt based their new genus on mere differences in outline and though Woodward did not regard these as generic characters, and Miller [N. A. Geol. & Pal. 1889, p. 548], obviously for like reasons, refused to recognize the genus, while Zittel cites it as doubtful, it is entirely evident from our present knowledge that the group, typically represented by Eusarcus scorpionis, is generically distinct from all its allies.
On this continent there is another locality, Kokomo, Indiana, which has afforded representatives of Eusarcus sometimes in gigantic examples. The first specimens were described by Claypole as Eurysoma newlini [1890, p. 259]. The term Eurysoma was soon after withdrawn by its author as preoccupied and was replaced by Carcinosoma. In 1894 another species (C. ingens) from the same locality was added and Eusarcus indicated as the nearest ally of the new genus, with the following qualification: "But the description of that genus [Eusarcus] mentions that the cephalothoracic portion is considerably narrower than in allied forms and that the terminal segment shows a widening and no trace of spiniform process. There are also several other minor points of difference." None of the differences here suggested by Claypole really exist, for our working material, which probably comprises nearly all Kokomo specimens ever collected, shows this carapace to have quite the same subtriangular form as in the Buffalo specimens, while both possess an ensiform telson. There are only minor differences between the Buffalo and Kokomo specimens; the latter are undoubtedly congeneric and the term Carcinosoma has to yield to Eusarcus.
From the study of the large collection of material representing the genotype we consider the genus as characterized by (1) the triangular carapace, (2) the marginal and forward position of the eyes, (3) the decrease in length of the walking legs backward, (4) the spinosity of all walking legs, (5) the broad elliptic to subcircular preabdomen, (6) the sharply defined, greatly lengthened, cylindrical postabdomen, (7) the broad and short, subtriangular metastoma, (8) the distinctive proportions of the segments of the swimming legs.
These characters, we believe, are correlated and shared by a number of species which thus constitute a well defined group. We have been able to satisfy ourselves as to their presence in Carcinosoma newlini Claypole (including C. ingens Claypole), save the form of the metastoma which has not been clearly seen. Woodward's elaborate description and excellent figures of Eurypterus scorpioides bring out all of these characters save the position of the eyes which were not observed. The inversely triangular form of the metastoma is particularly well established in that species. A like shield-shaped metastoma is assigned by Woodward to Eurypterus punctatus, known only by disjointed parts and regarded by him as closely related to E. scorpioides. Eurypterus obesus H. Woodward may be the young of E. scorpioides, a possibility suggested by the author of the species; at any rate, it strikingly exhibits the characters of Eusarcus, the last drawing published [1872, pl. 30, fig. 8] also showing the characteristic triangular carapace thus leaving only the supposed intramarginal eyes as a discordant feature to which we will return in another chapter. The Pterygotus raniceps H. Woodward, referred by its author to that genus on account of its marginal eyes, leaves no doubt in our mind as to the propriety of its reference to Eusarcus, on account of the triangular form of its carapace, the forward and marginal position of the eyes, and the subcircular outline of the preabdomen. Laurie properly compares his Eurypterus scoticus with Eusarcus scorpionis Grote & Pitt. It has the outline of body and the limbs of an Eusarcus. Further, the imperfectly known Eurypterus acrocephalus Semper (1898), a Bohemian form, belongs here. Its subtriangular carapace which gave the species its name and the broad, abruptly contracted preabdomen warrant this reference and Semper has correctly
 Figure 52 Metastoma of Eusarcus punctatus Salter. Natural size. (From Woodward |
 Figure 53 Eusarcus obesus (H. Woodward). Natural size. (From Woodward) |
pointed out the similarity of its species to E. scorpionis and E. scorpioides. Finally the Stylonurus (?) simonsoni Schmidt is distinctly an Eusarcus, as we have set forth in the appended footnote.[16]
The presence of the genus Eusarcus in the Frankfort fauna is demonstrated by various characteristic parts of the integument, viz, two forms of carapaces, cordiform metastomas so typical of Eusarcus, extremely broad and short tergites, the long conical postabdominal segments, a telson, and fragments with the characteristic ornamentation. The metastomas are probably the most conclusive of these, no other genus having furnished singularly broad and short subtriangular plates.
The two species here described are for the present entirely based on the carapaces and the other parts of the integument are noted below.[17]
The genus hence comprises the following species:
| Eusarcus scorpionis Grote & Pitt | E. raniceps (H. Woodward) | |
| [incl. E. giganteus Grote & Pitt] | E. scoticus (Laurie) | |
| E. newlini (Claypole) | E. acrocephalus (Semper) | |
| [incl. E. ingens (Claypole)] | E. simonsoni (Schmidt) | |
| E. punctatus (Salter) | E. longiceps nov. | |
| E. scorpioides (H. Woodward) | E. triangulatus nov. | |
| ? | E. obesus (H. Woodward) |
As minor characters which, however, also contribute to give Eusarcus its peculiar or even odd appearance and which seem to be present in all the species before cited, may be mentioned the strong development of the spines of the walking legs, the relatively great length of the seventh segment of the swimming legs and the peculiar surface sculpture, which in all representatives shows a strong tendency to become tuberculate instead of triangular-scaly as in the others, i.e. the scales are much smaller, more crowded and more or less circular in outline.
Three of the generic characters are closely correlated and combined. They indicate an attitude of the animal wholly different from that of Eurypterus. These are the triangular carapace, the frontal position of the compound eyes and the predominant size of the anterior walking legs. These characters demonstrate that Eusarcus raised the eyebearing front end of its carapace highest above the ground while Eurypterus brought its broad shovel-shaped frontal part down to the ground in walking.
Another peculiarity is intimately connected with this style of bearing the carapace. Though at first glance it is apparently of minor importance, it gives species of Eusarcus a very different aspect from those of Eurypterus and indicates a difference of habit in the two genera. In Eurypterus the walking legs are invariably bent backward in the fossil state, while in Eusarcus they are as invariably bent forward.[18] In the living animals their direction was downward in Eurypterus as well as in Eusarcus but while in the former the posterior spines are the longer, in Eusarcus the anterior ones were either longer or at least of equal length with the posterior. The greater length of the posterior row of spines in Eurypterus must have emphasized the effect of the greater length of the posterior legs in bringing the front of the carapace down and, likewise, the greater length of the anterior row in Eusarcus would have increased the effect of the greater length of the anterior legs and assisted in lifting up the front of the carapace. The position of the longer row of spines, however, will determine the side on which the walking legs come to rest when limply sinking to the bottom.
The difference in the walking legs finds its strongest expression in the fourth pair. In Eurypterus the fourth is not only longer and thinner than the others, but also lacks the spines, while in Eusarcus, it is the shortest leg of the last three pairs, though equally strong and, like the others, provided with spines on all segments.
Another difference consists in the form of the swimming legs. Corresponding to the plumper, heavier form of Eusarcus, these legs are more powerfully developed. The paddles are much longer and broader, while the preceding segments, connecting with the coxae, are much shortened and thickened, so that the eighth segment in Eusarcus is fully as long or even longer (in old individuals) than the 2–6 segments together. The latter segments are consequently, in their proportions and even in their form, entirely different from those of Eurypterus. In these characters the swimming leg of Eusarcus has become closely like that of larger species of Pterygotus such as P. buffaloensis.
Eusarcus scorpionis Grote & Pitt
Eusarcus scorpionis Grote & Pitt. Buffalo Soc. Nat. Sci. Bul. 1875. 3:1, pl. 1
Eusarcus grandis Grote & Pitt. Ibid. p. 17
Eusarcus scorpionis Pohlman. Ibid. 1881. 4:21
Eurypterus scorpionis Semper. Beitr. z. Pal. u. Geol. Oesterr.-Ung. u. d. Orients. 1898. 11:86 et seq.
Eurypterus scorpionis Seeman. id. 1906. 19:57
Not Eurypterus scorpionis Pohlman. op. cit. 1886. 5:29–30, pl. 3, fig. 3
Our description of this hitherto very imperfectly known species is based on the remains of 20 specimens, apparently all that have been thus far secured. Seven of these are entire, or nearly entire, specimens and one of them is a young individual. Among the fragments are some that prove that this inelegant squatty eurypterid attained to similar gigantic proportions as the associated Pterygotus. The material at hand permits us to give a fairly complete description of both the dorsal and ventral aspects and of the various appendages.
Description. The outline of the body is a very broad oval, acute anteriorly and broadly rounded posteriorly, where a tubular tail (postabdomen) of equal length is affixed, ending in a long, curved telson, of again half the length of the tail.
Cephalothorax. The cephalothorax is about as broad as long, its outline is bluntly subtriangular, the two lateral margins converging at an angle of about 50° toward the anterior end which is truncated. The base is but little longer than the lateral margin (about one thirteenth). The anterior margin is about one third as long as the lateral margin. The posterior margin bends gently forward in the middle and is well rounded and projects slightly at the postlateral angles. The lateral margins were moderately convex; the frontal line slightly emarginate. There is evidence that the carapace was relatively convex along the middle axis and that it remained so to the anterior margin or even culminated there, where the compound eyes were borne on the sides of this frontal snoutlike prominence. The compound eyes are kidney-shaped, apparently smooth, without recognizable facets, about one tenth the length of the carapace and situated at the antelateral corners of the latter. The ocelli, well shown in one specimen, lie a little behind the center of the carapace [pl. 29], and probably occupied the apex of the head shield. The doublure is narrow at the sides; along the posterior margin it is 2 mm wide in medium sized specimens.
Abdomen. The abdomen is broad and depressed in the anterior portion and narrow and tubular in the posterior portion, the two parts contrasting in a most striking manner. The dorsal side of the anterior preabdomen appears to have been entirely flat, but the middle third of the posterior part projects above the flat or slightly concave pleural portions and this median convexity grades into the round postabdomen. The ventral side of the preabdomen was more strongly and uniformly convex than the dorsal. In outline the abdomen widens so rapidly that at the third and fourth dorsal segments, where it is broadest, it is already more than twice as wide as the head shield at its base. With the next two segments it contracts abruptly to the postabdomen.
Preabdomen. The tergites are broad, short plates; those in the middle are five times as broad as long. First tergite much shorter than the others, its posterior margin parallel to the posterior margin of the carapace; anterior margin uniformly and deeply concave, the segment having a shape approaching a crescent; antelateral angles produced into blunt ears. In most specimens this plate is pushed under the cephalothorax, sometimes, as in the type, so much that only its posterior margin remains visible. Second tergite also very concave in front, its antelateral angles projected forward. Posterior margin with a low broad concavity in the middle. This and the following tergites are much longer in the lateral than in the middle portions.
The five sternites or ventral segments are strongly curved forward and convex, of relatively great length, the latter amounting to one fourth of the width in the typical middle plates of the series.
Operculum differing from the following plates in outline but little if any longer. Anterior margin not seen in perfect preservation, but the evidence at hand indicates that the antelateral angles were truncated and well rounded and the remainder of the margin straight transverse. Posterior margin notably less curved backward near the sides than the following sternites, but produced into two prominent blunt lobes at either side of the median cleft.
The other sternites possess a double curvature. They are strongly curved forward in the middle half. The anterior margin becomes so deeply concave on either side that a middle transverse line passing through the center of the last sternite will touch the interior edge of these sinuses. The antelateral angles are produced into prominent ears. Corresponding to the anterior margin the posterior margin shows two broad, well rounded lobes on either side of the broad median sinus. Postlateral angles obliquely truncated and rounded. The second sternite has also the posterior angles of the median cleft well rounded off, while in the succeeding plates the posterior margin is continuous.
As the specimen reproduced in plate 35, figure 5 shows, the sternites were not only very convex in outline, but also highly arched, forming a high ventral vault.
The postabdomen forms a slender tail that sharply contrasts with that of the extremely broad preabdomen. The curved telson spine combines with the long tubular postabdomen to produce the singularly scorpioid aspect of the tail.
The first postabdominal segment which closes the interval between the broad preabdominal and the following narrow segments resembles the former in the dorsal and ventral aspects, as in other eurypterids. It is a short ring, about three times as wide as long, contracting posteriorly by one third of its width. The other segments are practically tubular. Their relative length increases so strongly backward that while the second segment is not quite half as long as wide, the last is six times as long as wide. The numerous marginal wrinkles and the form of the median portion of some less compressed segments indicate that the section of the last segments was nearly or quite circular.
The telson is a curved, stout spine, half as long as the postabdomen or equal in length to the last two segments. Its first two thirds are gently, and the last third strongly curved downward. Its basal portion is swollen globularly on the ventral side and hollowed out on the dorsal, thus forming an articulation specially adapted to a strong up and down movement in the vertical plane. The compressed condition of the telsons in our material has not permitted a clear view of the section but the keellike projections which appear on the lateral view indicate that the spine was probably four-sided. The edges of the keels are serrate.
Appendages. The chelicerae have been seen in position in two specimens [pl. 32] and one well preserved chelicera has been found detached [pl. 31]. These preoral appendages were the only prehensile organs of the animal; they are, therefore, of relatively large size. If the separate chelicera belongs to the specimen alongside which it lies—of which there is
 Figure 54 Eusarcus scorpionis Grote & Pitt. Ventral view of swimming leg of right side, and the coxa of that of the left side; the metastoma; operculum and the two following sternites. The female opercular appendage is partly preserved [see diagram, text fig. 55]. Text figure 57 is a diagram from the swimming leg here shown. Natural size. The original in the State Museum |
Figure 55 Outline sketch of the incomplete female opercular appendage of the preceding figure, with the sutures of the pentagonal pieces and of the sternites the pincers and a part of the basal segments are folded backward.
The walking legs are all relatively short but massive and are provided throughout with very long, stout, curved spines. The first pair is very short and project a little at the tips beyond the margin of the carapace; the second is the longest of the series and the following two pairs again decrease in size, the third being but little shorter than the second, while the fourth is shorter by about one third. In old individuals [pl. 33, fig. 2] the spines on the first leg attain one third the length of the whole member.
The coxa has been seen only in the leg referred to. It is here elongate, widens toward the base and is about as long as the following segment. The distal part is drawn out into a curved neck bearing the manducatory edge on its inner side. The teeth, which form a decreasing series, are long and sharp. Just above the first is a large round scar which may be the base of a much larger tooth at the head of the series, such as is found in other eurypterids. At the end of the series is a small round node which may correspond to the finely haired cushion which Holm observed on the coxa of the first walking leg and which he considers as possibly corresponding to the epicoxite of the following legs. The posterior portion of the coxa is partly lost as shown by the broken edge. The next segment is short and broad, about as wide as long, while the third, the longest of the series, is twice as long as wide. The following segments decrease rapidly in length and at a lesser rate in width. The terminal segment is spiniform. The spines, two of which are borne on each segment, save the first two and the last, increase in size regularly to the distal spines which are the longest.
 Figure 56 Diagram of ventral view of right swimming leg of Eusarcus. m, metastoma; the figures indicate the segments |
The detached walking leg consists of seven segments. Its short and thick form and the composition of seven segments indicate that it was one of the first pair of walking legs. None of the following legs have been seen entirely free, but the combined evidence of our specimens leads to the inference that they consisted of eight segments each, as in Eurypterus.
The swimming leg, corresponding to the plump form of the animal, is of massive proportions and furnished with a large paddle. The seventh and eighth segments forming the latter, are greatly lengthened and broadened and the segments connecting this paddle with the coxa are shortened and swollen for the reception of powerful muscles, held together by strongly interlocking articulations and, as their frequent plastic preservation shows, were covered by a thick periderm. Compared with the swimming leg of the species of Eurypterus this leg makes the impression of a much stronger, but less active and movable organ. The coxa has not been seen entirely free. Enough, however, is shown to indicate that it is of a rhomboidal outline, like that of Eurypterus, differing in that it is relatively higher and shorter [pl. 32]. The gnathobase is not preserved in the specimen cited. The second segment is not short and ringlike as in Eurypterus, but cup-shaped, widening rapidly distally. It is connected by the narrow ringlike or wedge-shaped third segment to the ringlike fourth segment. In an old
 Figure 57 Eusarcus scorpionis Grote & Pitt. Portion of dorsal view of left swimming leg. Natural size. Original in State Museum |
individual [text fig. 57] the three segments mentioned form a powerful spherical part of the leg. The fifth segment is ringlike on the underside of the limb, widens out and is extended anteriorly on the upper side. Near the center of the flaring upper portion of this segment the next, sixth, segment is inserted. This appears from both sides as a triangular, or originally rather conical body, the distal basal surface of which is deeply emarginate on the posterior side and extended on the anterior, so as to fit into the deeply emarginate basal portion of the seventh joint. The latter is by far the broadest segment of the limb and nearly as long as the following, the palette. It is subrectangular in general outline, its length is one fifth longer than the width, the proximal and distal sides both deeply notched for articulation. The upper angle of the proximal side is evenly rounded, the lower much produced to meet a corresponding notch in the preceding segment. The lower part of the distal side is produced into a triangular plate about one third as long as the segment and separated from it by a transverse suture. The other upper part of the distal margin is nearly straight. The eighth segment is a very long oval, twice as long as wide, the distal end being the more slender. The terminal segment is subcircular in outline and relatively large.
Figure 58 Diagram of dorsal view of left swimming leg
The metastoma is heart-shaped in outline and relatively short. The frontal margin is the longest; it seems to be slightly emarginate, but the preservation is not clear enough to determine this point. Length and width of plate nearly equal. The antelateral angles are well rounded and the sides contract in a gentle curve to the blunt posterior extremity.
Genital appendages. Of these only the female have been seen in two examples. In the older of the two the appendage begins with two triangular (or subpentagonal) basal members, not seen in the younger individual, as the sutures which separate them from the opercular plates are not developed. These plates inclose an elongate sagittate base similar in shape to that of Pterygotus buffaloensis. At the posterior angles of the latter two semicircular lobes are observable which probably covered the genital openings. From it proceeds the slender middle portion which is convex along the median line and flat along the borders. The distal extremity is seen in the younger specimen. Here it consists of two converging obtuse pieces with parallel inner and converging outer sides. The basal portion which is sagittate in the older individual is rounded or inversely heart-shaped in the younger [pl. 33, fig. 3]. The organ was slender and relatively long; in the larger specimen it extends, incomplete as it is, to the third sternite. The appendage of the second sternite has not been observed.
Ornamentation. The ornamentation of this species is characterized by the small size, but immense number and round circular form of the scales and tubercles. The carapace uniformly bears small tubercles, giving it a shagreen surface. The coxa, the metastoma and the muscular joints of the walking and swimming legs have somewhat larger scales most of which have the form of slightly tilted disks with the anterior segment cut away or submerged in the periderm, the posterior portion being raised. The tergite of a mature individual bears rather widely scattered, larger semicircular to low triangular scales which terminate rather abruptly or become fewer and smaller over the posterior doublures but continue on their overlapped anterior parts. On the sternites the scales are arranged in distinct bands, the anterior halves of the plates being covered with such a densely crowded mass of small semicircular scars that the naked eye fails to discern them. These increase in size to the middle of the sternite where they form a zone of larger semicircular to crescentic scars which are less densely arranged and become farther separated posteriorly until they almost entirely disappear above the doublure. Between these larger scales numerous small ones, often of microscopic size, are interspersed. The opercular plates differed from the other sternites in being almost entirely covered with the larger scales which are much more densely arranged than on the following plates, but are also lacking along the posterior border. The pentagonal and sagittate basal portions of the female genital appendage are ornamented like the opercular plate.
The postabdomen, as a whole, bears scales of the size and distribution of those on the tergites. They lengthen, however, posteriorly, approximately in proportion to the remarkable lengthening of these postabdominal segments until on the last segment they have become acutely pointed.
The telson is furnished with small circular scales on the swollen basal part and with long spinelike scales on the remainder.
TABLE OF MEASUREMENTS OF EUSARCUS SCORPIONIS [IN MILLIMETERS]  * When marked by asterisk only the portion protruding from the carapace is measured. Approximate measurements are in parentheses. |
Horizon and localities. Remains of this species have been found only in the Bertie waterlime quarries at Williamsville and Buffalo, N. Y.
Observations. The relative size of some of the largest fragments indicates that E. scorpionis reached at least a length of four fifths of a meter or 2–3 feet and thus belonged to the larger members of the eurypterid fauna of the waterlimes. It attained at least half the size of the giants of this fauna, the two species of Pterygotus.
Lacking the long and powerful pincers of those dangerous competitors, the principal or sole organ of defense and offense must have been the telson spine. In correspondence with this important function the postabdomen is so much extended that, with the telson, it greatly exceeds in length the remainder of the body. The curved position of the postabdomen in several specimens demonstrates the great flexibility of this part, while the downward curvature of the telson would make it a dangerous weapon when the postabdomen is thrown forward over the body, as this action would bring the tenninal spine into the position of an upturned sharp pointed scimitar.
There is a striking morphological similarity between the telson of Eusarcus and the tail of the scorpion and in view of this and the acknowledged close relationship of the merostomes with the scorpions, it becomes a fair question whether the tail spine may not have been equipped with poison glands. The preservation of the telson is not such as to permit the determination of the presence or absence of apical pores for the emission of the venom, or of the poison canal in the compressed spine. The form of the body of the animal does not suggest great agility, either in walking or swimming, but rather a habit of burrowing in mud or lying in wait for prey. In the absence of powerful prehensile organs of long reach, a quick dispatch of the prey must have been a necessity and this could have been well accomplished by an agile and venomous telson.
The table of measurements shows that the young individual exhibits interesting and probably phylogenetically significant differences from the adult in the general proportions of its body. The most notable of these is the relatively greater width of the preabdomen; for while in the young the proportion of length to width here is as 2 : 3, in the older specimens it is as 4 : 5. The postabdomen also is relatively wider or stouter than in the older individuals, while on the other hand, the relative lengths of preabdomen, postabdomen and telson to the total length have remained nearly the same. Still younger individuals would surely show other differences in these ratios. The cephalothorax which in our young and old individuals occupies about one sixth of the length and is a relatively insignificant part of the body, compared with the other eurypterids, has most probably lost in relative proportion during ontogenetic development.
Eusarcus newlini (Claypole)
Eurysoma newlini Claypole. American Geologist 1890. 6: 258
Carcinosoma newlini Claypole. Ibid. p. 400
Carcinosoma newlini Claypole. Ibid. 1894. 13: 78
Carcinosoma ingens Claypole. Ibid. p. 77
The highly bituminous dolomites of Kokomo, Ind., have afforded a species of Eusarcus which was described by Claypole first as Eurysoma then as Carcinosoma newlini. The peculiar character of this rock makes an unfavorable matrix and Claypole was successful only in outlining the body and legs of his species[19] but careful treatment of a series of these specimens has made it possible to elucidate in some measure the essential structures of the creature. The type specimen has not been located by us (cited as belonging to Mr Newlin of Kokomo), but we have before us several specimens brought together by the late Professor James Hall and now belonging to the museum of the University of Chicago, one of which agrees so closely with the figure of the type as to suggest its identity with the latter. Another specimen [pl. 39] in the same collection, both sides of which have been preserved, excels the type in the distinctiveness of several important features.
Besides these specimens we have two large individuals (one from the Hall collection, the other in the State museum) which correspond in size to Claypole's Carcinosoma ingens. This species was erected by Claypole for a specimen received from Mr Charles Smith of Akron, O. Here again the author furnished an outline sketch [reproduced in text fig. 60] and diagnosed the species by citing its differences from E. newlini. He says:
 |
 | |
| Figure 59 Original figure of Eurysoma newlini Claypole. (From Claypole) | Figure 60 Original figure of Carcinosoma ingens Claypole. (From Claypole) |
In the specific description the leading points of difference and those on which the definition rests are the greater size of the fossil and the smaller number of cusps or branches on the four anterior pairs of gnathopods.
The specimen measures 24 inches in length, whereas none of those from which the description of C. newlini was compiled exceeded 14. There are also only three cusps on the front edge of the first, third and fourth pairs of gnathopods, and four on the second pair. In C. newlini these cusps are sometimes 8 to 12 in number, and apparently in some cases project from the back of that organ, though this must be considered uncertain and against analogy.
There is, moreover, on the large paddles, no trace of the fringed or serrated edges which are so conspicuous in the paddles of C. newlini. They are perfectly even and smooth.
None of the differences cited seem to us to warrant any specific distinction, the different size being clearly due to age, since no important corresponding discrepancies in the proportional lengths of the parts of the body could be found to corroborate the supposed distinction. The cusps are, to our knowledge, of like number in all these Eusarci, all segments, save the first two and the last, bearing two spines each, the last forming a single spine. Both spines were of nearly equal size, as we have already observed in the generic description, but frequently only those of one side are observable, the others being either broken away, leaving their wartlike bases [pl. 33, fig. 1], or imbedded in the rock above or below the bedding plane on which the body rests. Of the two specimens of Eusarcus newlini before us, one [pl. 37] shows the spines of both sides and would hence correspond to E. newlini s. str., the other only those of one side and would hence have in this regard the character of E. ingens.
The last difference cited is the absence in C. ingens of the fringed or serrated edges "so conspicuous in the paddles of C. newlini." Much of the serrated appearance of the edges of the paddles in the eurypterids is due to a cracking of the thickened margin of this thin leaf like organ. For this reason one frequently sees in some specimens of this species an apparently very marked serration, while others have a distinctly smooth edge. The same is true of both E. newlini and E. ingens, E. newlini possessing, in reality but a very weakly developed serration.
The supposed differences between E. newlini and E. ingens are doubtless due to slight variations in preservation, but even if of actual existence, they could be of no more than varietal importance. We here refer all specimens of Eusarcus from Kokomo to one species which has the following characters.
Description. General form that of a rather short, posteriorly broad oval body (carapace and preabdomen) with abruptly attached tubular tail (postabdomen) of equal length with the body, and a rather short, stout tail spine.
Cephalothorax broader than long (proportion of length to width as 7 : 8 in the youngest specimen), the difference decreasing with increasing age, in the largest example being reduced to but one fourth of its earlier size; outline a regular triangle with truncated angles, the lateral margins moderately convex,[20] the posterior margin gently concave in the middle, almost straight. Posterior truncating line or postlateral angles very gently convex; frontal margin probably slightly emarginate between the eyes. The lateral eyes have been seen only in the largest specimen; they are located at the antelateral angles, are of bean-shaped outline and about one fifth the length of the lateral margin. Their structure has not been observed; nor have the ocelli been seen in any of the specimens.
Abdomen. Preabdomen relatively shorter than in any of the other species; a little longer than the carapace and nearly twice as wide; broadens in continuation of the lateral margins of the carapace to the fourth tergite, whence it contracts rapidly to the powerful postabdomen which is twice as long as the preabdomen and two fifths as broad.
The outlines of the separate tergites and sternites have not been distinguished with clearness and no separate plates observed; hence no detailed description of their form and relative dimensions can be given, but enough has been seen to prove that they do not differ materially from the corresponding parts of the better known E. scorpionis, although it is to be inferred from the relative smaller length of the preabdomen that the preabdominal plates were also relatively shorter. The first tergite would, from the evidence of the largest specimen, seem to have been at least eight times as wide as long. The posterior margins (which alone are seen owing to the more abrupt termination) are nearly straight in the anterior tergites but become distinctly concave in the middle of the last two plates; in the sternites they are throughout broadly concave in the middle and well rounded at the postlateral angles.
The gill plates are distinctly outlined in the smallest of the specimens [pl. 37,] and are of elongate, sublanceolate outline, rounded on the inner side and acutely pointed on the outer, slightly diminishing in size posteriorly.
The postabdomen appears disproportionately long; it is fully twice as long as the preabdomen. At the same time it is broader (one fourth as wide as long) than in other species and has altogether the appearance of a very powerful organ. The first segment completes the contraction of the oval portion of the abdomen as in the other Eusarci, thence the postabdomen is of nearly uniform width, contracting but one sixth to the posterior extremity. The first segment is a narrow ring with a strong forward bend, about four and one half times as wide as long. The next is of similar shape and rate of contraction, but four times as wide as long. At the postlateral angles it is slightly produced backward and its lateral margins are concave, indicating that it had the form of a concave truncated cone. The next, like the following, is of tubular form. The last four segments do not lengthen nearly as rapidly in this species as in Eusarcus scorpionis, the sixth being twice as long as the third and three fifths as wide as long.
The telson has been seen in but two specimens. In one of these it agrees with the figures given by Claypole of E. newlini and E. ingens in being short, stout and straight. Its length is one sixth that of the body and four times as great as its basal width. The basal fourth is slightly expanded or inflated, the remainder tapers regularly to a point. One of the specimens shows at the underside near the base a fragment of a flat-topped carina such as is found in the other eurypterids, suggesting that the section of the telson does not differ materially from that in other genera. No traces of marginal serrae are observable in our specimens.
Appendages. What appear to be the tips of the chelicerae or preoral appendages are seen in the largest specimen, the chelicerae having there remained in normal position. If this view is correct, these appendages were relatively large and strong.
The ectognathites or walking legs are here developed into stout and long organs which, except for the first pair, protrude far beyond the carapace and by their width give the impression of great strength and importance. This impression is still more emphasized by the great length of their curved spines. The first leg was the shortest, only its last two segments and their spines protruding. The second walking leg which is the longest, is exposed with six segments outside of the carapace; its exposed portion equals the carapace in length. The segments in this pair of appendages are about as long as wide; in the following legs they become increasingly shorter. The spines attain about one fourth the length of the ectognathites, the terminal clawlike spine being the longest and the others decreasing in proximal direction. Each exposed segment bears two spines of apparently somewhat different length which all curve inward. Of the next swimming leg about one segment less protrudes and the segments are also shorter, the exposed part being thereby shorter by one sixth than that of the preceding leg. The fourth pair is shorter than the second by at least one third; its segments, however, are broader than long by about one third, so that again five segments protrude.
The swimming legs are distinguished by great length and width; turned back they reach the beginning of the narrow part of the postabdomen (line of third postabdominal segment). The coxae of the legs have been seen only in outlines too faint and obscure for exact description. One of these is indicated on plate 38. The manducatory edges which are the most resistant parts of the gnathobases are also seen on plate 37, as rows of fine teeth. The segments forming the arm or pole of the swimming legs are rather short, ringlike and broad with intricate articulations, none of which however is well preserved. The seventh and eighth segments form a much lengthened but little broadened blade; the seventh segment is about one and one half times as long as wide and occupies nearly one third of the length of the arm beyond the coxa. The proximal extremity is deeply notched for the articulation with the preceding segment; the lobelike plate, marked off from the inner distal margin by a suture, is rounded and occupies half the width of the segment. The palette is a long subelliptical body, twice as long as wide; its distal extremity slightly convex, the inner nearly straight. It carries at its distal extremity a nearly circular claw of relatively great size (one fourth the length of the palette) so snugly fitted in a corresponding notch that it is discerned with difficulty. The edges of the blade are furnished all around with small serrae.
The metastoma has not been seen.
Genital appendages. The only trace of a genital appendage seen is a small oval area which suggests an immature female appendage.
Ornamentation. The preservation of most of the material is such that the substance of the integument is a finely puckered carbonaceous film obscuring all former surface ornamentation. In the smallest specimen the impression of the postabdomen shows small elongate elliptic scales of the character of those in E. scorpionis [pl. 39]. On the sternites and the carapace of the same specimen traces of small circular markings are also observable, suggesting that on the whole, the ornamentation of this form was little different from that of E. scorpionis.
Horizon and localities. All representatives of this species have come from the Kokomo waterlime horizon at Kokomo, Indiana.
Remarks. A survey of the specimens figured[21] shows that they form a fairly continuous series of later growth stages, the first two of which correspond in size to Claypole's E. newlini, the last two to his E. ingens. In the introductory remarks we have already given reasons for uniting the two names. These can be briefly restated as consisting in the absence of the distinguishing characters cited by Claypole and in the agreement of the dimensional proportions in the smaller and larger individuals. There appear to exist a few actual differences between the smallest and
TABLE OF MEASUREMENTS OF EUSARCUS NEWLINI  Parentheses imply approximate measurements.
¹ Claypole records E. newlini as measuring 10–12 inches. The original drawing measures 5¼ inches and can therefore be safely considered as being a one half reduction. |
largest specimens, which can be more plausibly explained as growth differences rather than varietal distinctions. There are the somewhat greater width of the carapace and more convex lateral margin, the greater thickness of the walking legs and swimming legs in the largest specimen, all of which combine to give the latter a more robust and less agile appearance. The same age difference we have observed in other eurypterids, as has been noted more fully in another place.
E. newlini as here defined unquestionably belonged to the giants of the race and lagged little, if at all, behind E. scorpionis in size. Not less than three of the few specimens known indicate individuals of two feet or more in length.
The species differed from E. scorpionis in being built still more compact and sturdy. This is shown in the relatively shorter and broader preabdomen, the shorter and especially broader postabdomen and the shorter, stouter and probably straight telson. The posterior contraction of the preabdomen is more abrupt and the outline of the preabdomen and carapace combined more broadly oval posteriorly. The walking legs are stouter and provided with longer spines; the swimming legs reach farther back (principally on account of the greater contraction of the preabdomen) and the postabdomen is notably broader. The cephalothorax has grown somewhat in proportion to the body, probably on account of the greater stoutness of the appendages for which it has to serve as basis of attachment.
Eusarcus (?) cicerops Clarke
Eurypterus? cicerops Clarke. N. Y. State Mus. Bul. 107. 1907. p. 307, pl. 5, fig. 10; also pl. 5, fig. 7
Description. The original description of this species which was based on a single specimen is:
This diminutive head shield is remarkable for the extraordinary development of the compound eye lobes which are anterior and very prominent and though the shield has a diameter of only 4.5 mm, the ocellar mound is fully developed. So unusual is the aspect of this specimen that it can not be assigned to any of the other species here noted, and though entirely immature, it is given a distinctive designation.
Later collections have furnished a few more specimens of like size exhibiting the same unusual characters as well as somewhat larger specimens which would indicate, if properly referred here, a remarkable change of characters in the ontogeny of this form. We shall first describe the type and then note the later changes.
The type of the original description [pl. 36, fig. 4] is a small broadly triangular carapace so unusually broad that its length to width is as 2 : 3. The lateral margins in their general direction converge to the protruding front of the carapace and possess a gently sigmoidal curvature, the posterior two thirds resembling projecting cheeks while the anterior third is concave. The postlateral angles are acute. The carapace is highest between the eyes, the ocellar mound being on the apex. The posterior portion of the head is strongly depressed in all specimens, rising abruptly to the upturned lateral borders, and gradually from the base forward. A thickened filiform border bounds the lateral margins and a narrow, flat, depressed border the posterior margin. The projecting frontal margin is flat or slightly elevated.
A very striking feature of the carapace is the pearllike projecting eyes placed very far forward and intramarginal, lying in the pit of the concave curve of the lateral margin. The visual surface is distinctly seen in several specimens [pl. 36, figs. 3, 4, 8]. It is crescent shaped and narrow. The ocellar mound which is situated on a line connecting the posterior extremities of the compound eyes is, like the latter, characterized by extreme prominence, and besides by its remarkably large relative size.
Only one specimen has been found that can give a clue to the original form of the abdomen. Corresponding to the diverging lateral margins of the head and its broad basis, this is also broad and widens much toward the posterior portion of the preabdomen, after which it probably contracted rapidly to the telson.
The boundaries of the tergites are but very faintly seen and it is possible that the specimen has suffered contraction by pressure.
The postabdomen and telson have not been seen in place but a curved telson with attached last postabdominal joint [pl. 36, fig. 7] has been referred here provisionally, partly because it could not be placed with any other species and partly because the head and abdomen of E. ? cicerops suggest its reference to Eusarcus and this telson points also to the same genus. Indeed, we consider the presence of this telson good evidence of the presence of a Eusarcus in the Otisville fauna, and therefore as supporting the reference of the species here described to that genus.
The carapace of E.? cicerops, as exemplified by the holotype, corresponds to that of Eusarcus in the following characters: its typically sub triangular outline with slightly projecting cheeks, the oval form and highly anterior marginal position of the compound eyes. The great width of the preabdomen is also a feature comparable only to Eusarcus.
The immature aspect of the holotype has been mentioned in the preliminary description. It finds its most distinct expression in the relatively large, oval eyes, their forward position and the prominence of the ocelli. It is shown in this paper that the earliest growth stage of Eurypterus maria, and to some extent also of members of other genera, is distinguished by its broad carapace, and thus the form of the head of E.? cicerops also emphasizes this impression of immaturity. It is, however, to be noted that while the specimens are quite probably not mature forms, their size excludes them from the larval or nepionic stage, of which the immature features mentioned here are characteristic. Moreover we have a specimen of larval dimensions and features [pl. 36, fig. 9] whose size indicates that the other specimens are at least of neanic age. If this be correct, they allow a fair conclusion as to the mature form which, as the largest of the specimens [pl. 36, fig. 2] indicates, retained the outline of the head and the position of the eyes, but lost the pearllike prominence of the eyes and the sigmoidal curvature of the lateral margins. The scarcity of the young individuals in the Shawangunk grit at Otisville allows the inference that the species was very rare in that fauna and adults have therefore not yet been obtained.
The carapace of the nepionic specimen [pl. 36, fig. 9], measuring but 1.2 millimeters, is of striking, or rather grotesque appearance by virtue of the following features:
- The broadly triangular outline
- The spinelike prolongations of the frontal and genal angles
- The immense, diverging eyes
- The strong median crest
- The broad margin
In this nepionic individual the relative width of carapace is much greater than in the type. The impression of excessive width is, however, hightened by the lengthening of the genal angles parallel to the base of the head. These horizontal genal spines, together with the equally produced third frontal angle of the triangle, serve to strongly emphasize the triangular aspect of the head. The frontal projection is the forward continuation of a strong median crest extending forward from the base. The lateral margins exhibit the sigmoidal curvature and the cheeklike convexity of the posterior portion as in the following stage.
The compound eyes are oval in form, of great size (about one third the total length of the head), strongly divergent and placed in the middle of the head instead of forward and farther inward from the margin than in the older individuals. The fact that they are surrounded by a deep depression seems to indicate that they were originally quite prominent, thereby drawing the surrounding test downward with them in becoming depressed to the level of the carapace. The ocelli have not been discerned. Finally the carapace exhibits a broad thick margin on all three sides, possibly a broad doublure on the under side.
It is easily seen that this larval form, notwithstanding its own peculiar characters, shares its most important features with the larval stages of other eurypterids. This is especially true of the large size of the eyes, the great width of the head and the presence of a median crest. The acute lobes of the angles are a character peculiar to this larval form and perhaps in line with the spinose processes of the larval forms of many crustaceans. The position of the compound eyes in the middle of the head may be of phylogenetic significance and indicate the secondary acquirement of the frontal position of these eyes in Eusarcus. It should be also noted that the convergence of the eyes in the mature form is directly reverse to that in the larval stage, obviously a consequence of the later adjustment in position of the compound eye to the converging frontal margins.
Measurements. The length of the type (carapace) is 3.2 mm; its width 4.8 mm; the width of the carapace of the original of plate 36, figure 5 is 4.5 mm; the greatest width of the abdomen is 6.1 mm. The largest carapace referred to here [pl. 36, fig. 2] measures 7.4 mm in length and 10.6 mm in width. The telson figured in connection with this species measures about 27 mm in length and 5 mm in basal width.
Horizon and locality. Very rare in the dark shales of the Shawangunk grit at Otisville, N. Y.
Eusarcus (?) longiceps nov.
Plate 84, figures 1–6
Description. Carapace semielliptical in outline, about as wide at the base as long, the lateral margins nearly straight and slightly converging forward to the antelateral angles. Frontal margin well rounded; posterior margin straight transverse and genal angles acute, apparently produced a little sidewise. Eyes marginal, small, about one fifth the length of the carapace, situated at the antelateral angles, the visual surface occupying the whole eye node; the latter apparently without facets. Ocelli large, situated between the lateral eyes. The carapace was either smooth or the original ornamentation is obscured.
Horizon and locality. Frankfort shale (Schenectady beds) at Schenectady.
Remarks. We have comprised under this species a number of carapaces of strange aspect, which in outline do not agree exactly with any of the Siluric genera. The eyes, in form and position, suggest the genus Eusarcus, but the position of the ocelli near the frontal margin between the compound eyes is a feature not observed in any genus. It would seem that this form had gone even beyond Eusarcus in the concentration of the sense organs at the front, in adaptation to its habit of covering itself with mud. The type specimen [pl. 84, fig. 5] measures 18 × 15 mm, its lateral eyes are about 4 mm long, the largest specimen observed is 31+ mm long; its width is indeterminable, the sides being folded under; the eyes measure 7 mm.
Eusarcus triangulatus nov.
Plate 84, figures 7–9
Nine carapaces which have in common the broad, short, subtriangular form and the forward position of the marginal lateral eyes, bear a close resemblance to the carapace of E. scorpionis from the Bertie waterlime. The largest of these [pl. 84, fig. 7], which is also the most distinct, has been selected as the type of the species E. triangulatus.
Description. Carapace broadly subtriangular in outline, twice as broad as long (length of type, 20 mm, width, 43 mm), the lateral margins gently convex in the anterior third, forming a blunt frontal angle. Posterior margin straight transverse or broadly convex forward; genal angles acute. The lateral eyes are marginal, situated one third of the length of the lateral margin from the frontal apex, small (one seventh to one eighth the length of the side), bean-shaped, the visual surface apparently occupying the entire node. No facets seen. Ocelli situated in the middle of the carapace.
In several specimens the first tergite is found attached to the carapace. This is broad and short, about seven times as wide as long. In another specimen [pl. 84, fig. 9] the preabdomen and the proximal portion of a swimming leg are also preserved.
The carapace and first tergite were smooth or have only small, scattered tubercles.
Horizon and localities. The Frankfort shale (Schenectady beds) at Schenectady (Dettbarn quarry), Duanesburg and Rotterdam Junction.
Genus DOLICHOPTERUS Hall
Hall erected Dolichopterus as a subgenus of Eurypterus, citing as its distinguishing characters: the development of the "palette" (ninth segment), the less dilatation of the natatory feet, the form of the metastoma, and of the "central footlike organ" (genital appendage). It has been accorded full generic rank by later authors, with perfect propriety, we feel sure, although it remained monotypic until Holm referred two metastomas from the dolomitic shale of Rootziküll, Island of Oesel,[22] to this genus. The Bertie waterlime of Williamsville, near Buffalo, which has furnished the genotype, has afforded the carapace of a second species, here described as D. siluriceps, and the shale of the Shawangunk grit at Otisville has furnished a third species which sheds much interesting light on this rare and little known genus. We have named this last species D. stylonuroides because the carapace has all the characteristics of that of Stylonurus [pl. 46, fig. 13] in its subrectangular outline, broad doublure with frontal triangular plate on the underside and broad rim of the dorsal side, position, relative size and form of the lateral eyes. Its most peculiar features are, however, its swimming feet which appear beset with leaflike plates, the last segment being tripartite and consisting of three lanceolate plates. It is not difficult to recognize in its structure a further development of the peculiar lobelike lengthening of the segments of the last pair of legs noticed in D. macrochirus and to see in the tripartite extremity of the leg the result of the strong development of the ninth segment characteristic of Dolichopterus, the middle lobe representing the ninth, the lateral ones the preceding eighth segment. The same development of lobes is shown on the preceding pair of legs in the genotype and the leg retained in D. stylonuroides still further resembles that balancing leg as the last segment is developed into a spine, flanked by two lobes.
This interesting combination of a Stylonurus carapace and Dolichopterus leg in the same specimen suggests the question of the relationship of these two genera. A comparison of the two shows that Dolichopterus is more closely related to Stylonurus than to Eurypterus as a subgenus of which it was regarded by Hall and with which it has been associated by later authors. The similarity in the outlines of the carapace is manifest; they also have in common the distinctness and great width of rim, while the doublure in D. macrochirus is much narrower than in the typical Stylonurus. The eyes differ in both genera from those of Eurypterus in being relatively much larger, placed as a rule further forward and having their visual surfaces so extended that the extremities of each edge approach each other [pl. 45, fig. 1 and S. myops]. The relationship of the two is strikingly brought out in the form of the metastoma. The elongate subrectangular outline in D. macrochirus is well shown in plate 45, figure 3. It obviously corresponds in length to the much elongated carapace and the long coxa of the swimming leg. The two metastomas figured by Holm are of like shape. Laurie has succeeded in tracing the outlines of the metastomas of two species of Stylonurus [text fig. 64] and they exhibit the same form as that of D. macrochirus. Similar metastomas are quite common in the Otisville beds, where two species of Stylonurus and one of Dolichopterus occur. The form of this organ appears to furnish an excellent criterion of generic unity, as here demonstrated among the species of Eusarcus and Pterygotus, and it is inferred that like metastomas in different genera are strong evidence of close relationship.
Further, we have here shown that at least one subgenus of Stylonurus, viz, Ctenopterus, is characterized by long, straight, relatively thin, closely arranged spines. The same feature is repeated in D. macrochirus [see drawing of type, Hall, pl. 83A, fig. 1 and, here, pl. 45, fig. 3].
This similarity of the legs continues in the last two pairs, and shows itself in the great lengths of the fourth and fifth segments.
Finally the slender, gradually tapering abdomen of Dolichopterus with its winglike epimera [pl. 43] is also more suggestive of Stylonurus than of Eurypterus or any other of the genera of the eurypterids. We suspect that the telson will prove to be styliform in Dolichopterus as in Stylonurus.
The main difference between Dolichopterus and Stylonurus is in the development of the distal parts of the last pair of legs; in Dolichopterus these are broadened and beset with leaflike lobes, while in Stylonurus they are narrow and greatly lengthened. The preceding pair of legs is also furnished with lobelike appendages in Dolichopterus and is free of such in Stylonurus.
The question of the phylogenetic relation of Dolichopterus to Stylonurus, Drepanopterus and Eurypterus has been fully dealt with in the introductory chapter to which we here refer.
Besides the three species of Dolichopterus from the New York rocks thus far mentioned, the Bertie waterlime at Litchfield and the Shawangunk grit at Otisville have each furnished a type represented only by the carapace; D. testudineus and D. otisius; and the Frankfort shale has afforded the fragmentary remains designated D. frankfortensis and D. latifrons.
From the waterlime beds of Litchfield we have a swimming leg, which possesses in general the characters of Dolichopterus but has a greatly differing palette or terminal segment. The latter is elongate oval and strikingly resembles the palette of Pterygotus. As the palette in Pterygotus is the eighth segment, while that of Dolichopterus is the ninth, this similarity can hardly be more than the result of convergence. This limb is as far different from that of the genotype, D. macrochirus, in one direction, as that of D. stylonuroides is in another. In this the relative compactness and strength of the swimming leg of D. macrochirus is carried to extreme, in the other the tendency of D. macrochirus to the development of broad lobelike appendages.
These few species together indicate a greater variability in the characters of this genus than is shown by other genera.
The genus is at present represented by seven American and two European species, viz:
| D. macrochirus Hall | D. stylonuroides nov. |
| D. frankfortensis nov. | D. testudineus nov. |
| D. latifrons nov. | D. laticeps (Schmidt) |
| D. siluriceps nov. | D. sp. Holm[23] |
| D. otisius Clarke |
Dolichopterus macrochirus Hall
Plate 35, figure 1; plates 40–45
Dolichopterus macrocheirus Hall. Palaeontology of New York. 1859. 3:414, pl. 83, fig. 1; pl. 83A, fig. 1
Professor Hall based his description of this genus Dolichopterus and of its genotype D. macrochirus upon a single specimen from the waterlime at Williamsville. This is now in the American Museum of Natural History and is unique in its state of preservation, for it can be lifted bodily out of the matrix and exhibits both sides; these were so accurately figured by Whitfield that new figures can add only immaterial features. Unfortunately, however, this type lacks the greater part of the postabdomen and telson and retains only the proximal portions of the limbs, save the last pair, besides being incomplete in such other important points as the posterior portion of the metastoma, the opercular appendages and the operculum itself. It is therefore extremely gratifying that later collections in this State have afforded three more specimens of this extremely rare species which happily supply the desired information. The most important of these is a specimen from the famous locality of Wheelock's hill, Litchfield [pl. 43]. This retains the postabdomen and telson and furnishes important information as to the limbs and the metastoma. Another specimen, from Forge Hollow near Water ville, N. Y., now in the American Museum, exhibits beautifully the second, third and fourth postoral limbs with their spines and lobes, showing novel characters especially as to the structure of the fourth limbs. Finally, the museum of the Buffalo Society of Natural Sciences contains a specimen with well preserved appendages. With the help of this material the following description of the species can be given:
Description. Body medium sized, relatively slender, with long appendages. Carapace and preabdomen of about equal length, postabdomen larger by one half than preabdomen, and telson as long as carapace.
Carapace of quadrangular outline, relatively long (length to width as 6 : 7); the frontal margin broadly emarginate, the rounded anterior angles slightly projecting, the lateral margins parallel and nearly straight for more than half their length from the base. Doublure narrow. Lateral eyes large, about one fifth the length of the carapace, situated close to the anterior angles, less than their length distant from the anterior margin, and about that distance from the lateral margin. The protuberance is oval, and apparently surrounded halfway by the visual surface.
The preabdomen is little shorter than wide (length to width as 5 : 6) attaining its greatest width at the third tergite and contracting thence gradually to the postabdomen. Judging from the specimens reproduced on plates 42–44, the segments of the preabdomen were highly arched. In the flattened condition, they are about six or seven times as wide as long. Their posterior margin is broadly concave in the middle.
The operculum is a very long plate; it is hardly more than three times as wide as long. The other sternites seem to have overlapped to more than half their length and were hence also relatively long plates.
The postabdomen is the longest division of the body. It surpasses by one half the preabdomen, decreases gradually in width to nearly one half, while at the same time the length of the segments is doubled, in the first segment the width surpassing the length five and one half times, and in the last not even one half times (actual proportion 10 : 54; 20 : 28). The postabdominal segments are furnished with distinct epimera that increase in width with each succeeding member, and are prolonged into short spurs, except on the last segment where they are produced into long, rounded lobes. The posterior doublure is wide, amounting to nearly one half the width of the first segment.
The telson is narrow and long, apparently little shorter than the postabdomen. It contracts rapidly for a short distance from the anterior end, then it continues slender, or increases again slightly to the point which is abruptly rounded. The section is triangular. The dorsal surface is flat or slightly convex, the ventral produced into a flat-topped carina. The edges are sharp and marked by oblique incisions which, toward the extremity, grow into sharp teeth.
The preoral appendages of the cephalothorax have not been seen. The first three pairs of postoral appendages form a series of remarkably stout walking legs that increase in length posteriorly and decrease very little in width distally. They consist of short, ringlike segments, all of which, except the three basal ones, bear a pair of extremely long, curved spines [pl. 45, fig. 3]. The terminal spine or claw also is distinguished by its great length. It is flanked by the almost equally long spines of the last segment. The fourth limb, which has been known hitherto by its basal portion only, displays quite as peculiar characters as the last limb. In length it is intermediate between the third walking leg and the much elongated swimming leg, begins rather slender and becomes gradually wider distally. Though it terminates in a very long and strong claw, thus having the appearance of a walking leg, this claw is not flanked by the two like spines on the last segment as in other eurypterids, but by two broad bractlike lobes. Tracing these legs proximally, the impressions of further bractlike appendages are seen on the inner side [pl. 45, fig. 2, 3], in the places where in the preceding legs the long paired spines are found. Since the opposite sides of the same leg show these bractlike lobes, it is apparent that they represent a modification of the spines of the preceding limbs.
Hall fully recognized that the last postoral limb differs from the corresponding organ of all other eurypterids in the development of the ninth segment into a broad expansion like an oar blade. These last limbs are not only very long, for when fully turned back they would have nearly reached the penultimate postabdominal segment, but also rather flexible and expanded in all segments, most markedly however in the last four. The coxa of this leg, which is fairly well shown in the type and still better in the specimen from Litchfield, differs in outline from those of other eurypterids being much longer in anteroposterior direction.[24]
The coxa is subrhomboidal in shape (its short posterior side only half as long as the long inner edge), with a long curved neck leading to the manducatory edge. The second and third segments are short, ringlike, especially so the third, while the fourth is distinguished from all others by its length, it being twice as long as each of the two following segments and four times as long as the preceding one. It is twice as long as wide. The fifth and sixth segments are of subequal dimensions, each nearly one fourth longer than wide. The seventh and eighth segments are broad and relatively short, their longitudinal and transverse diameters being about equal. Their outer edges are obscurely serrate. The lobe of the seventh segment which is narrowly triangular in Eurypterus, is here produced into a leaflike process, which in length equals the segment. The eighth segment, which is the palette in Eurypterus and Pterygotus, is in this genus of similar form as the preceding segment. The ninth segment, the small "claw" in other eurypterids, has here assumed the bladelike shape of the eighth segments in Eurypterus and Pterygotus. It is oval in shape, with its extremity somewhat drawn out, longer than the preceding segments, one and one half times longer than wide. Its outer margin is coarsely serrate, the serrations directed obliquely forward and convex on the outer side. The metastoma has been described by Hall as "lyrate, with the anterior margin cordiform." Its length is more than half that of the carapace, its greatest width (in the anterior fourth) one half of its length. It decreases slightly in width posteriorly. Its lateral margins are nearly straight or but slightly concave. Its posterior end is transversely truncate, slightly emarginate in the middle.
 Figure 61 Dolichopterus macrochirus Hall. Outline sketch of the ventral appendages of the type specimen. Natural size |
The opercular appendage of the female is seen very imperfectly in Hall's type. It is better shown in the specimen in the museum of the Buffalo Society of Natural Sciences [pl. 44]. It is similar to that of Eurypterus, differing mainly in the greater length and less curvature of the paired terminal pieces. The proximal portion has not been distinctly seen. Traces of the pentagonal areas and the inclosed hastate proximal extremity of the first unpaired lobe are observable. The appendage extends beyond the middle of the second sternite, but the specimen is probably stretched. In Hall's type, which is clearly contracted in the preabdomen, it extends to the middle of the fourth sternite.
No surface ornamentation has been observed except linear rows of high, circular scales on the proximal segments of the last two pairs of limbs.
| Measurements of type: | millimeters | |
| Length of carapace | 57.5 | |
| Width of carapace | 70 | |
| Length of eyes | 13 | |
| Length of metastoma | 32+ | |
| Anteroposterior length of coxa of last leg | 43 | |
| Length of swimming leg beyond carapace | 125 | |
| Length of preabdomen | 68+ | |
| Width of preabdomen | 74 | |
| Length of tergite | 15+ | |
| Length of operculum about | 25 | |
| Length of opercular appendage about | 52 | |
| Length of first postabdominal segment unknown; width of same about | 52.5 | |
Some measurements complementary to the preceding are afforded by the Litchfield specimen.
The metastoma is 30.4 mm long; 16.5 mm wide ad maximum and 11 mm at the posterior end.
The coxa of the last limb is 35.7 mm long on the inner side and 22.4 on the posterior. The swimming leg measures 128.7 mm; its eighth segment is so much contracted that the original length was about 130 mm.
The preabdomen is 53 mm long and 54 mm wide. The postabdomen measures 90 mm in length; it is 53 mm wide at its anterior end and 28 mm at its posterior end. The first sternite is 12.5 mm long, the last 19.5 mm. Of the telson 44 mm are preserved; its initial width is 15.5 mm.
Horizon and localities. The four known specimens of this rare species, from Williamsville, Litchfield and Waterville, were obtained from the Bertie waterlime.
Remarks. Hall clearly set forth the peculiar characters of this species in the original description. He says "this species is distinguished by its robust, elongate body, the long straight-sided carapace, very anterior eyes, strong and thick jointed anterior feet, and extremely long swimming feet, with the great development of the terminal palette and the little dilation of the two preceding joints. The form of the postoral plate is very remarkable, though its posterior termination is unknown; the appendage is more prolonged and of a different form, and the adjacent articulation is very peculiar; and there are distinctive features in the maxillary plates."
The exceedingly long spines of the first three pairs of legs, the bractlike appendages of the fourth pair, and the great anteroposterior extension of the coxae of the last legs may be mentioned as further peculiar characters.
The powerful, long spined first legs indicate that D. macrochirus was an able walker and the bract-covered next pair of limbs, as well as the great elongation of the last pair, serve to demonstrate that it was likewise a powerful swimmer.
In consequence of the active use it made of its swimming legs, the species appears to have developed strong internal keels [pl. 43] within some of the segments corresponding to the entapophyses or internal keels and bars in recent arthropods, serving as attachment bases for powerful muscles.
Dolichopterus frankfortensis nov.
Plate 83, figures 9–14
The presence in the Frankfort shale fauna of at least one species with the characteristics of a Dolichopterus is demonstrated by a considerable number of carapaces and several metastomes. We refer these all for the present time to one species.
Description. Carapace subquadrate; length and width about equal; frontal margin very bluntly angular in the middle; lateral margins nearly straight; slightly bulging in the posterior half; posterior margin broadly concave. Antelateral angles very prominent, a little larger than a right angle; genal angles well rounded in the type, rectangular in other specimens. A distinct flat or beveled border follows the lateral margin, and a narrower one the frontal margin. The lateral eyes are situated at the antelateral corners, relatively small (about one fifth the length of the carapace), semicircular to semielliptical in form, the straight diameter forming the inner margin. The visual surface was apparently crescentshaped. The ocelli were situated on a line with the posterior extremities of the lateral eyes. The ornamentation [see pl. 83, fig. 10] consists of closely arranged, low flat nodes.
Horizon and localities. Frankfort shale at Schenectady (Dettbarn quarry), Aqueduct, Rotterdam Junction and Duanesburg, whence the type and some of the best specimens came.
Remarks. We have about a dozen carapaces, mostly from Schenectady, which agree in general outline and position of the lateral eyes, but show slight variations in the character of the frontal margin which in some exhibits a rather sharply protuding middle projection while in others it is somewhat emarginate. It is, however, quite probable that these latter variations from the form of the frontal margin of the type, are due to lateral and oblique compression and folding of the thin integuments.
This species must have attained considerable size, for one carapace [pl. 83, fig. 14] was about 69 mm long and 62 mm wide at the frontal angles. The type specimen measures 8 mm by 8 mm.
A metastoma has been found which recalls that of D. macrochirus.
Dolichopterus latifrons nov.
Plate 83, figures 15–16
Description. Carapace of small size, spade-shaped in outline, broader by one half in front than at the base, its greatest width equal to its length; the frontal margin marked by a flat or beveled border, most produced in the middle, and posteriorly bounded by a straight transverse projecting edge; antelateral angles rounded; lateral margins divergent forward and gently convex; posterior margin slightly concave, the edge slightly raised; genal angles obtuse; lateral eyes large, about one third the length of the carapace, situated in the antelateral angles and submarginal, with semicircular eye nodes and crescent-shaped (when compressed) visual surfaces; ocelli situated between the posterior portions of the lateral eyes. No ornamentation has been observed.
Horizon and locality. Two specimens have been found in the Frankfort shale at Schenectady, N. Y.
Remarks. The carapace described here differs from the preceding species mainly in the posterior contraction. In this feature it agrees closely with D. otisius, a species from Otisville. The eyes in position and form are typically those of Dolichopterus.
The type specimen measures 14 mm in length, 14 mm in frontal width and 9 mm in basal width. The eyes are 4.5 mm long.
Dolichopterus otisius Clarke
Plate 46, figures 1–8
Pterygotus? otisius Clarke. N. Y. State Mus. Bul. 107. 1907. p. 308, pl. 6, fig. 6, 7
Description. The original description of this species is:
An elongate subquadrate head with eyes anterior, far apart and just within the margins; ocellar mound well back between the posterior horns of the eye crescent; surface quite smooth. The specimen figured and one other of similar character are all that is known of this species.
Although later collections have afforded us upward of 30 specimens of this odd species, none of them retains more than the carapace and two body segments. The generic determination is therefore dependent as before on the character of the carapace and suffers the resulting lack of positiveness. The better and varied preservation of the new material which ranges considerably in size, permits however a greater elaboration of the description.
The carapace is subquadrate in outline, narrowing slightly toward the base. The frontal margin is the most convex, increasing in prominence with advancing age and in the largest specimens becoming distinctly angular. The antelateral angles project but are well rounded; behind them the carapace contracts somewhat rapidly and widens again in the posterior half forming low cheeklike projections of the lateral margins. The posterior angles are subrectangular and but little rounded. The posterior margin is gently concave or straight. A fine thickened filiform rim surrounds the lateral and anterior sides. The produced frontal part of the carapace is flat or depressed and continuous with a flat border on the sides. The remaining part appears to have been moderately elevated and to have culminated behind the ocellar mound. The doublure of the underside is broadest in front, corresponding in extension to the flat frontal border and is narrower on the sides. It possesses one to two deep wrinkles that cross the frontal portion transversely. The lateral eyes are situated in the anterior corners, near the margin, separated from the latter by about twice the width of the flat border. They are very large (one third the length of the carapace), prominent, semielliptic in outline, the outer side convex, the inner straight. The visual surface is crescent-shaped, situated on the outer slope. The supporting ridges are apparently very strong, especially so along the convex outer margin. In one specimen the surface exposed is ornamented with low, small, very closely arranged circular tubercles.
The first tergite is a very short band of subequal length, nearly eight times as wide as long. The second tergite is twice as long and considerably wider.
Measurements
| Type: | millimeters | |
| Length of carapace | 15.2 | |
| Width of carapace | 15 | |
| Length of eyes | 4.6 | |
| Smallest specimen observed: | millimeters | |
| Length of carapace | 5.1 | |
| Width of carapace | 5.1 | |
| Length of eyes | 1.9 | |
The largest specimen observed is but slightly larger than the type.
Horizon and locality. Shawangunk grit at Otisville, N. Y.
Observations. The carapace of this species does not bear the typical expression of any genus; its aspect is rather suggestive of several; viz, Pterygotus, Slimonia and Dolichopterus. The type specimen in which the outline is more rounded than in the rest may be well compared with Pterygotus, while the approach of the eyes to the anterior corners, the quadrangular outline of the carapace and the frontal rim are quite likely to suggest Slimonia. The lateral eyes, however, although possessing an elliptic outline as those of Pterygotus and Slimonia, are quite obviously not furnished with a visual surface extending over the whole prominence as in those genera, but with one that is crescent-shaped as in the genera more closely allied to Eurypterus. This, taken in connection with the fact that the eyes are distinctly within the margins, necessitates a reference to the latter group of genera. This granted, the identification of the species with Dolichopterus becomes imperative, for the squarish outline, the position of the eyes in the corners, their relatively large size and the broad border of the carapace are features which are combined only in the genotype of Dolichopterus. We may add that the semielliptic outline of the eyes, also a very characteristic feature in all well preserved specimens of the present species, are repeated in D. macrochirus.
The youngest specimens are of special interest in this connection; for they lack the frontal angular extension which constitutes a difference from D. macrochirus although it is only a further development of the broad frontal rim common to the young of D. otisius and to the genotype. The young [pl. 46, fig. 4] is hence still more like Dolichopterus: in fact it has the typical expression of that genus in every particular.
Dolichopterus siluriceps[25] nov.
Plate 26, figure 3
Eusarcus scorpionis Pohlman. Buffalo Soc. Nat. Sci. Bul. 1886. v. 5, no. 1. p. 30, pl. 3, fig. 3
Description. In 1886, as above cited, Pohlman figured and described as belonging to Eusarcus scorpionis, a carapace that subsequently came into the possession of Prof. J. S. Newberry and this specimen is now in the museum of Columbia University (no. 3078).
Eusarcus scorpionis has a subtriangular carapace and it is apparent that this specimen, both in outline and the position of the eyes, belongs to Dolichopterus; at the same time it differs in its proportions specifically from the genotype D. macrochirus. In the carapace of the former the proportion of length and width is as 6 : 7, but here it is as 6 : 8.5, as a result of which the carapace of D. macrochirus looks squarish in outline, while this is broadly quadrangular. The relation of these carapaces is similar to those of Eurypterus remipes and E. lacustris. A further obvious difference consists in the marked contraction of the carapace in the anterior half and the resulting strongly converging anterior lateral margins in E. siluriceps.
The carapace of this species furnishes the following description:
Hexagonal, basal side the longest, curving broadly forward in the middle third; the lateral margins are very slightly divergent behind and more strongly convergent in front; the greatest width of the carapace being at the point of change of direction in the lateral margins. The postlateral angles are nearly right angles, very slightly rounding, while the very obtuse antelateral angles are broadly rounded, and are connected in front by a nearly straight or slightly concave anterior margin. The eye tumescences are broken out. Their cavities occupy nearly one fourth the length of the carapace, are broadly oval in shape and only 4 mm distant from the margin, at the antelateral angles. The ocelli have not been seen. An obscure tumescence which may have borne them is noticeable midway between the posterior portions of the lateral eyes. The doublure of the carapace does not seem to have been very broad on either the front or the sides. The surface is smooth.
Measurements. The carapace measures 81 mm in length along the median line and 85 mm where it is longest. It is 77 mm just in front of the eyes, 108.5 mm in its widest part and about 99 mm at the base.
Horizon and locality. Rare in the Bertie limestone at Williams ville, N.Y.
Observations. There is no other species in our faunas, save a small form from Otisville, with both similar outline of carapace and like anterior position of the eyes. Nor are we aware of European forms that invite comparison.
Dolichopterus (?) testudineus[26] nov.
Plate 57, figure 2
Description. A single uncompressed carapace from the Bertie beds is of small size, obovate in outline; the greatest width, which surpasses the length by one tenth, forward of the middle, just behind the eyes; thence the well rounded margins converge to a point in front; and they also converge rather strongly toward the base of the head shield, so that the latter is but three fourths as wide as the widest part of the carapace. As the lateral and frontal margins form an evenly rounded curve, no indications of antelateral angles are present, but a slightly projecting anteromedian or frontal angle is produced. The posterior margin is broadly concave in the middle and gently curved forward at the genal angles, so that the latter are obtuse and rounded.
By breaking away parts of the head shield a broad doublure is exposed. It passes all around to the genal angles, where it is abruptly cut off; the posterior margin being lined by a very narrow doublure. The surface of the carapace appears to have been uniformly convex, but just behind the frontal angle a rather sharp transverse ridge is observed.
As in the other species of Dolichopterus, the compound or lateral eyes are situated within the margin where the frontal and lateral margins unite. They are of great size (one fourth the length of the head shield) and separated by a distance equal to their own length. The ocular node is semicircular in outline; the inner margin straight, the outer a semicircle; its top flat or slightly depressed; the visual surface is crescent-shaped. The ocellar node is situated between the lateral eyes; ocelli not seen.
| Measurements | millimeters | |
| Length of carapace | 27 | |
| Width of carapace | 30 | |
| Width of base | 22.5 | |
| Length of lateral eyes | 7 | |
Horizon and locality. Bertie waterlime; Schooley's farm, east of Crane's Corners, town of Litchfield, Herkimer co., N. Y.
Remarks. This species, as represented by the single carapace, is quite similar to D. otisius [comp. pl. 46, fig. 2]. It differs from the latter mainly by the greater extension of the frontal portion and by the more pronounced posterior contraction of the carapace. The frontal transverse ridge or fold observed in the species is also seen in D. otisius.
The same locality has also furnished a swimming leg [pl. 57, fig. 1] which while distinctly belonging to a Dolichopterus, is greatly different from that of D. macrochirus, the only fully known congener occurring at Litchfield. We consider it therefore probable that it belongs to D.testudineus. Its most striking character is the development of the palette or ninth segment, which is very elongate elliptic, with an obliquely truncate base and which much resembles the palette (or eighth segment) of Pterygotus. The preceding segments are very broad, indicating a powerful organ, but lack the distinct development of lobelike appendages seen in D. macrochirus and still more striking in D. stylonuroides.
The fourth and fifth segments are well shown, the latter with the typical elongate development seen in Dolichopterus. The sixth and seventh are pushed so into each other that it is impossible to clearly separate them; the eighth is of cup-shaped outline and shorter than the corresponding segment in the genotype, but, as indicated by wrinkles, probably much compressed longitudinally.
Dolichopterus stylonuroides nov.
Plate 46, figure 9–14
A rare and interesting species from Otisville is represented in the collections by three carapaces and one more complete specimen retaining besides the carapace one entire swimming leg and three tergites. From these specimens the following description is derived.
Description. Body small, probably slender. Carapace spadelike in outline, as long as wide, widest on anterior fourth and contracting by about one fourth to posterior margin; frontal margin convex, quite uniformly rounded, sometimes slightly produced in the middle; antelateral angles well rounded; lateral margins gently concave; posterior margin slightly concave in the middle. A broad, level rim of approximately uniform width surrounds the frontal and lateral margins, while the underside of the carapace shows a still wider doublure most expanded in the middle of the front where a triangular lobe extends backward; and which also broadens toward the posterior margin. The lateral eyes are large (one fourth length of carapace), kidney-shaped and situated in the antelateral corners, one third the length of the carapace from the frontal margin and half way between the median line and the lateral margin. The visual surface is crescent-shaped. The ocelli are very distinct, and situated on a circular tubercle between the anterior parts of the lateral eyes. A longitudinal ridge seems to extend thence backward.
Abdomen. The first tergite is very short (six times as wide as long), closely parallel to the posterior margin of the carapace. The following tergites are two to three times as long and slightly increase in width.
Appendages. The swimming leg, the only appendage observed, is relatively short, twice as long as the carapace. The coxa and second segment have not been seen. The third is short and ring like, the fourth tubular, long, slender (two and one half times as long as wide) and slightly curved. The next is again shorter (half as long as preceding) and also tubular, slightly widening distally. The sixth is of the same length with the fifth and elongate pentagonal in outline. Like the following segments it bears two broad leaflike spines of greater length than the segment. The seventh and eighth segments are of similar length but broader; apparently of inverted cuplike outline but obscured by the overlying spines, which give the terminal part of the leg the appearance of a bud-bearing twig. The last joint is apparently subdivided into three bractlike lobes, the middle of which is the longest.
No traces of the ornamentation of the test are shown.
| Measurements | millimeters | |
| Length of carapace | 10.8 | |
| Greatest width | 10.2 | |
| Least width | 8.2 | |
| Length of eyes | 2.4 | |
| Length of first tergite | 1.0 | |
| Width of same | 8.4 | |
| Length of third tergite | 2.2 | |
| Width of same | 9.4 | |
| Exposed length of swimming leg | 16.5 | |
| The largest carapace observed measures | ||
| Length of carapace | 17 | |
| Greatest width | 16.3 | |
| Least width | 15 | |
| Length of eyes | 4 | |
Horizon and locality. In the Shawangunk grit of Otisville, N. Y.
Observations. We have already noted the stylonuroid features of the carapace of this species. The spadelike form of the carapace is also shown by Stylonurus symondsi (Salter) [see Woodward, 1872, pl. 21, fig. 4] and S. macrophthalmus Laurie. Neither of these two species, however, has as long a carapace as D. stylonuroides. D. macrochirus has a shorter carapace and is a much larger species.
Genus STYLONURUS Page
The genus Stylonurus was proposed by Page in 1855 in a paper read before the British Association [see Bibliography]. It was based on a single species (S. powriei) figured and named the following year in his Advanced Text-Book of Geology. Only a single specimen, not very favorably preserved in sandstone, has been recorded and although Page's not very correct figure and explanation have been followed by Woodward's elaborate description and careful illustration, this genotype is still incompletely known. Indeed, when the investigation of a considerable number of species revealed to us the presence of divisions of undoubted subgeneric rank, it remained doubtful with which of these the genotype belongs and which of the divisions therefore represents Stylonurus sensu stricto. A conventional conception of the genus has been created by the restorations made by Woodward and by Beecher. Woodward's restoration is based on the species S. logani, and Beecher in his restoration of S. excelsior had to follow Woodward in nearly all important features, only the carapace, the chelicerae and first pair of legs of S. excelsior being known.
It is especially on the character of the limbs that the most important subgeneric differences are to be based; it is therefore necessary to subject the genotype and the restorations mentioned to a critical review in regard to these structures. Woodward's conception of the relative lengths of the legs obviously resulted from a combination of the two specimens of S. powriei and S. logani. The former furnished the evidence for the conclusion that the last pairs of legs are "about equal both in length and breadth" [1872, p. 123], for it was the only specimen known to him retaining these legs; while the specimen of S. logani which retained the last long leg and several of the anterior limbs scattered about the carapace, furnished the evidence for the two pairs of short limbs in his restoration. Woodward figured in front of these two feelerlike appendages which in Beecher's restoration of S. excelsior are replaced by a first pair of short walking legs, the latter together with a chelicera having been successfully prepared by Clarke [1888, pl. 26A].
An example from the dark shales at Otisville has shown by preparation a series of four legs on one side and this species exhibits in the formation of its carapace the typical characters of a Stylonurus. The structure of this species, S. cestrotus, has suggested a different conception of the limbs of Stylonurus, for, (1) the last two legs are of distinctly different length, (2) the second and third pairs of legs are so long as to form a progressively growing series with the fourth and fifth pairs. The question then arises whether Stylonurus had been incorrectly understood or whether the Otisville form represents a new and different group.
A survey of the 13 species, cited below as falling under the head of Stylonurus by virtue of the characters of their carapaces and abdomina, shows that, besides the original representatives of the genus, S. powriei and logani, of only four species are specimens known that retain sufficient fragments of the legs to indicate their structure. These are S. macrophthalmus and S. elegans Laurie, S. cestrotus Clarke and S. scoticus Woodward. Taken together these demonstrate two important facts; (1) that the legs increased in length quite regularly backward instead of being divided sharply into two different sets as represented by Woodward and Beecher: an anterior one of very short legs and a posterior one of exceedingly long ones, (2) that there are three distinct types of legs among species referred to this genus.
As already stated, Woodward seems to have combined the aspects of his specimens of S. powriei and S. logani to effect his restoration of S. logani; the former furnishing the two long legs, the other the preceding two short pairs. In considering the question of the two "subequal" long pairs of swimming legs, it may be observed that the specimen 
Figure 62 Stylonurus elegans Laurie. Second to fourth legs of right side. (From Laurie) of S. cestrotus which retains both in full length, distinctly shows that there was a considerable difference in the two pairs, the fourth being shorter in total length by about one sixth, and each of its segments a little shorter than the corresponding one of the fifth [pl. 49, fig. 6]. In S. elegans Laurie, where the last two pairs are also shown, this difference is still greater [text fig. 62][27] and the same is suggested by Laurie's drawing of S. macrophthalmus [1892, pl. 2, fig. 10]. It would seem then that all specimens of Stylonurus, except the original S. powriei, exhibit a distinct difference in length between the last two pairs of legs. From the two figures of S. powriei, published successively by Woodward [1865, pl. 13, fig. 1; 1872, pl. 21, fig. 1], it also becomes obvious that that specimen must possess the same difference, for the segments of the fourth pair are throughout shorter than those of the fifth, but as noted above, the single type is poorly preserved, was therefore apt to mislead and is not conclusive in this regard. In view of the fact that Drepanopterus, which clearly leads
Figure 63 Stylonurus logani H. Woodward. Original figure. (From Woodward)
phylogenetically to Stylonurus, exhibits a much greater difference between these two leg pairs, it is a fair deduction that such difference also existed in typical Stylonurus, though less pronounced and perhaps in various gradations.
A further question relating to the legs, suggested by the Otisville specimen of S. cestrotus, is whether the second and third pairs were as short and as nearly equal in size as represented by Woodward and Beecher. Here again all the types which retain these legs; those of S. cestrotus, S. macrophthalmus, S. elegans and S. ornatus, give direct evidence that they also formed a posteriorly increasing series, the last being the longest and that, on the whole, they were much longer than represented in the restorations. The specimen of S. logani [text fig. 63] which served as the basis of the restorations exhibits a fragment of two segments of one of these legs attached to the body and is surrounded by two (three in first figure, 1864) detached anterior legs. The smaller of these undoubtedly represents the first pair of postoral limbs, as clearly indicated by its rapid contraction and the shortness of the segments. As the first pair Woodward introduced antennae and constituted as the second pair what we believe to be obviously the first, while the other, which has about twice the length of the former, to us represents the second pair. The third pair is only represented by the small fragment still attached. It is quite clear that there is considerable difference in length between the first and second legs and a still greater difference between the second and third legs. The relative lengths of the first and second legs are well shown in Laurie's type of S. macrophthalmus [text fig. 64] and the relative great length of the third pair is evident in S. elegans [text fig. 62] where it nearly equals the fourth pair and surpasses it in width. Looking back again, in relation to these legs, to Drepanopterus, the ancestor of Stylonurus, we find that there the first three pairs also form a series increasing in length backward.
The combined evidence, then, of the material at present available is that the legs formed an approximately continuous series, the anterior members being longer than hitherto supposed and the last two not so greatly surpassing the others in length and not of so nearly equal length. On the basis of these facts we have drawn a new reconstruction of S. excelsior, although only the first pair of legs of that species are known, using mainly our specimen of S. cestrotus for this reconstruction.
 Figure 64 Stylonurus macrophthalmus Laurie. Original figure, showing four legs and metastoma. (From Laurie) |
The gradually lengthening series of legs suggests to us that they, all combined, were functional in crawling, the long hinder pairs, on account of their stronger curvature and backward direction, reaching the same level as the shorter forward pairs with their terminal claws, thereby carrying the body as it is carried in nearly all crustaceans and arachnoids, on four or more pairs of legs.
There is a difference of opinion as to whether the last pair or pairs were the more active in swimming, as in the other eurypterids, or the first three pairs, as suggested by Beecher. On one hand analogy with the other eurypterids would indicate the use of the last pair of legs as swimming organs, and it would constitute a wide departure if this group reversed the functions of the fore and hind limbs. On the other hand, these hind legs show none of those characters which naturally accompany a swimming function, such as a widening of the joints and an intricate articulation insuring rigidity of the legs, while the preceding legs, in some species as S. cestrotus, are provided with a dense fringe of contiguous spines or bristles well adapted to broaden the swimming surface of the limbs. To the first leg of S. excelsior which is the only one observed, paired flat spines are attached whose form suggests their adaptation to swimming. We are disposed to regard all legs as adapted for crawling. Though in some species the forelegs served as swimming organs, the long posterior ones were mainly active in pushing the animal forward.
In another group of species again the forelegs do not differ in relative length and character from the walking legs of Eurypterus. The typical representative of this group is S. logani. This leads us to the discussion of the subdivisions of Stylonurus, distinguishable on the basis of leg structure. On comparing the figures of S. logani and S. macrophthalmus [text fig. 65] with those of S. cestrotus and S. elegans, it is at once evident that in the former the forelegs are not only relatively smaller and narrower than in the other but are also provided with only one pair of spines each, as in Eurypterus, while in the latter group these legs are relatively much longer, more powerful and furnished with a contiguous series of long spines, each segment carrying a greater number of spines than two, a character apparently not repeated in other genera.[28] A third group is represented by S. scoticus Woodward. In this, the single limb known (obviously one of the last pair) is greatly broadened from the beginning and is distinctly a swimming leg. The similarity of this swimming leg to that of Eurypterus would suggest a reference to the latter genus if the other characters of the animal were not so manifestly stylonuroid. Still the species is not a typical Stylonurus but distinctly a later and more specialized form. This is shown not only by the swimming leg but also by the large hooked, winglike epimera of the postabdomen and the sculpture of the tergites. It demands recognition as representing a subdivision of Stylonurus.
The genotype is not sufficiently known to establish its relationship to any of the three subdivisions here proposed.
Subgenus A is typically represented by S. logani and S. macrophthalmus. Its first three pairs of legs retain the characters of those of Drepanopterus and are like those of Eurypterus, i. e. relatively short and stout and furnished with two curved, strong spines on each segment. S. ornatus Laurie also belongs in this group.
We suspect that also Eurypterus scabrosus, a curious form described by Woodward [1887, p. 481] from the Lower Carbonic shales of Eskdale, belongs here, although the specimen does not retain the fifth pair of legs, whicht are of critical importance in the distinction of Eurypterus from Stylonurus.[29] The great length and slenderness of the preceding legs, however, are a character only found in Stylonurus, but not in any of the species of Eurypterus known to us. Likewise the coarse, roundish, tuberculate sculpture of the posterior margins of the tergites is more suggestive of Stylonurus than of Eurypterus.
Subgenus B. This is typically represented by S. elegans Laurie and S. cestrotus Clarke. Its second and third pairs of legs are relatively much longer and furnished with more than two pairs of long, less curved spines which are vertical on the lower side of the segments. Besides the species mentioned, another form from the Pittsford shale, S. multispinosus, only known from two of its legs, clearly belongs here; and we surmise that S. excelsior also, from the character of its first legs which alone are known, should be brought under this group. In case this structure should not be found in Stylonurus proper, the term Ctenopterus may be applied to this group. The leg from the Utica shale figured by Walcott as Echinognathus clevelandi, shows a like structure in exaggerated form and may prove to represent the group, in which case the term Echinognathus would take precedence. At present the employment of the latter term would be unwarranted as the body of the Utica form may be entirely different from that of Stylonurus.
Subgenus C. This is represented alone by S. scoticus. Its differential characters are the flat broad last pair of legs, the greatly enlarged winglike epimera of the postabdomen and the emphasized sculpture of the posterior margin of the tergites. The short club-shaped telson is also notable. The carapace and the form of the abdomen are as in Stylonurus. We propose for this group the term Tarsopterus.
Subgenus D. Finally Drepanopterus is, in our opinion, not more differentiated from the typical Stylonurus than S. scoticus, though it stands quite at the other end of the phylogenetic line. Drepanopterus longicaudatus nov. is a form distinctly intermediate between Stylonurus and the type of Drepanopterus. On account of its phylogenetic importance in the development of Stylonurus we have treated this division as a separate genus.
The majority of the species can not at present be definitely referred to any of these groups as only their carapaces are known. The following is a provisional synoptic table of the species:
| Subgenus A. (Stylonurus s. st.) | |
| S. logani H. Woodward | S. powriei Page |
| S. macrophthalmus Laurie | Stylonurus (?) scabrosus (H. Woodward) |
| S. ornatus Laurie | |
| Subgenus B. (Cternopterus) | ||
| S. cestrotus Clarke | S. multispinosus nov. | |
| S. elegans (Laurie) | (?) | S. excelsior Hall |
| Subgenus C. (Tarsopterus) | |
| S. scoticus H. Woodward | |
| Subgenus D. (Drepanopterus) | |
| S. lobatus Laurie | S. bembycoides Laurie |
| S. pentlandicus Laurie | S. longicaudatus nov. |
| Indeterminate species | |
| S. megalops Salter | S. beecheri Hall |
| S. ensiformis H. Woodward | S. ? limbatus nov. |
| S. symondsi (Salter) | S. myops Clarke |
Among the American species only group B (Ctenopterus) and group D (Drepanopterus) have thus far been recognized, the former with one, the latter with two species. The subgeneric relations of the four other American species: S. excelsior, S. beecheri, S.? limbatus and S. myops remain undetermined.
Stylonurus (Ctenopterus) cestrotus Clarke
Eurypterus? cestrotus Clarke. N. Y. State Mus. Bul. 107. 1907. p. 307, pl. 3, fig. 8–10
The original description of this species reads: "Of this species we have only enough to satisfactorily establish its difference from other forms—the two specimens here illustrated. Both show the peculiarly ornamented frontal border of the cephalon which carries a row of denticulations. One of these specimens conveys a satisfactory idea of the form of the body, and presents the ventral aspect but there is some uncertainty in regard to the number of segments and though evidences of four pairs of legs are present the structure of these is not apparent. The head shown in figure 10 indicates that the compound eyes are large and very far forward. It is entirely probable that when this species becomes better known it will have to be excluded from the genus Eurypterus."
The larger collections acquired since this date and the development of the counterpart of the first of the two specimens figured in the preliminary paper, have afforded sufficient data to form a fairly accurate conception of this most peculiar type.
Description. Body of small size, slender and terete, all parts being noticeably elongate.
Carapace elongate oval in outline, broadest in the posterior fourth, whence it contracts to half the width at the frontal margin. Its length and greatest width are but slightly different. The lateral margin is most convex at the broadest portion of the carapace which is frequently somewhat expanded into a kind of cheek. It becomes gently convex more anteriorly and passes rather abruptly at the antelateral angles into the more or less projecting frontal margin. The postlateral angles are well rounded and the posterior margin is deeply concave in the middle. The frontal border is furnished with a row of 8–16 acute denticulations which are longest in the middle and decrease in size toward the lateral ends. The serrae are directed obliquely upward. The lateral margins are bordered by a thickened rim.
The upper side of the carapace is highly sculptured. Its most prominent parts are the big bulging compound eyes. The portion of the carapace in front of these is flat but rises in the middle to a large subcircular mound, bearing tubercles of greater size than those forming the ornamentation of the rest of the carapace. Oval, sharply set-off cheeklike ridges extend backward from the lateral eyes to near the posterior margin, and from the intervening depression, midway between the lateral eyes, rises the very prominent small mound bearing the ocelli. The underside of the carapace bears a broad and thick doublure which is widest along the frontal margin and there exhibits a deep concentric furrow.
The lateral eyes are very large (one third the length of the carapace), forming projecting elliptical bodies that lie near the lateral margin and parallel to the latter in their major axis, thus converging strongly forward. Their posterior extremities lie approximately on the transverse bisecting line. The visual surface is crescent-shaped and narrow; its horns approach each other on the inner side. The eye mound overtops the visual surface considerably and forms apparently an overhanging ridge on the inner side of the visual surface so that the latter frequently disappears entirely in compressed specimens.
The ornamentation of the carapace consists of small tubercles which reach their largest size on the frontal mound and cheeks and extend over the whole carapace, including the eye mounds, in uniform density.
The abdomen is slender. It expands gradually to the fourth segment whence it contracts again as gradually to the long and slender postabdomen. The greatest width is probably about one fourth greater than that of the carapace. The preabdomen is longer by one third than the carapace, and the postabdomen is but little longer than the preabdomen. The tergites are short plates with nearly straight anterior and posterior margins, while the sternites exhibit strongly curved posterior margins, the middle being strongly concave and the postlateral angles well rounded and produced backward. Traces of a marginal line of tubercles on the tergites have been observed and it is possible that the whole surface was tuberculate.
The telson has not been observed in position, but it is quite probable that a slender spine, found in association with these remains, belongs to this species since it fully corresponds to the form of the postabdomen.
Appendages. The chelicerae and first pair of legs have not been seen. Of the second pair but four segments of the specimen could be exposed without destroying the following legs, and of the third pair also a portion of a fifth segment. These exposed portions show that the legs were long and slender, the third still somewhat surpassing the second in length; thus the second to fourth legs continuously increase in length backward. The fourth and fifth segments, and presumably the following ones, are furnished with a series of straight, slender paired spines, about 6–9 pairs on each segment. The fourth and fifth pairs of long legs were not of equal size, but the fourth shorter by one eighth. The latter, fully reflexed, would reach the last postabdominal segment and the fifth leg the telson. The coxae of these legs are not exposed; the first and second segments, however, are partly seen and can be recognized as consisting of short rings; the third is somewhat longer, while the fourth is the longest and broadest of all. It is two and one half times as long as the third. The sixth is again shorter by one third while the seventh and eighth are distinguished by again increasing in length and decreasing notably in width. The terminal spine is short and stout with incurved point. All the segments, including the terminal spine, carry sharply elevated longitudinal ridges.
On account of the obvious distortions of all specimens we refrain from giving measurements of the parts of the animal beyond the relative dimensions cited above.
The metastoma and genital appendages have not been observed in place.
Horizon and locality. One of the rarer forms in the Shawangunk grit at Otisville, N. Y.
Remarks. S. (Ctenopterus) cestrotus stands apart from all its allies in a number of characters that show it to be an aberrant form. The most notable of these are the frontal prolongation of the carapace, the frontal row of denticulations, the strongly tuberculate mound behind the latter and the submarginal, forward position of the eyes. It is hardly to be doubted that these characters together with the slender form of the body and the length of the legs indicate that it was an active species and not a mud groveler. The elongate outline of the carapace it has in common with S. excelsior. Both these species probably belong to the same subgenus, Ctenopterus.
Different degrees and directions of compression have produced a strikingly varying series of aspects of the carapace, some of which are here reproduced, since these specimens serve to bring out certain other features. In some we have indicated the direction of compression by pointers. In a few [pl. 50, fig. 4–6] the typical aspect is so completely changed by the preservation that without intermediate stages they would surely be taken for. representatives of different species.
There is a distinct similarity by convergence between this form and certain species of the trilobite Dalmanites that finds its most pregnant expression in the frontal row of denticulations duplicated in the subgenera Odontocephalus and Corycephalus, in the bulging frontal mound, recalling the frontal lobe of the glabella, and the large, widely separated crescent-shaped eyes. We can hardly go amiss in attributing this similarity less to an accidental coincidence in fugitive characters than to an adaptation to like conditions or similar habits.
Stylonurus (Ctenopterus) excelsior Hall
Stylonurus excelsior (Stylomurus in error) Hall (Martin). N. Y. Acad. Sci. Trans. 1882. 2: 2
Stylonurus excelsior Hall. N. Y. State Mus. 36th An. Rep't. 1883. p. 77, pl. 5, fig. 1
Dolichocephala lacoana Claypole. American Philosophical Soc. Proc. 1883. 21: 236, pl. 3
Stylonurus excelsior Hall. American Assn. Adv. Sci. Proc. 1884. 33: 421
Stylonurus excelsior Hall & Clarke. Palaeontology of New York. 1888. 7: 158, 221, pl. 26, 26A
Stylonurus lacoanus Beecher. American Jour. Sci. 1900. 10: 145, pl. 1
Only two specimens of this species are yet known. One a natural external mould of the complete carapace from the Catskill beds at Andes, Delaware co., N. Y., is in the possession of Rutgers College and is the type of Hall's original description. Another fragmentary carapace from the same formation in Pennsylvania, the original of Claypole's description, is now in the National Museum. Clarke succeeded in developing on the underside of the latter, a chelicera, one of the first pair of legs and the coxae of two legs of the succeeding pairs.
Both these specimens and the discovered appendages have been fully described by Hall and Clarke in Palaeontology of New York, volume 7, pages 158, 221, to which the reader is here referred for the details.
Professor Beecher subsequently selected S. excelsior for restoration on account of its gigantic dimensions, supplying the missing parts from the British species S. logani and S. powriei, and the American S. beecheri. The discovery by the authors of a specimen of S. cestrotus at Otisville retaining all save the first pair of legs, and the fact that S. excelsior is, according to the form and character of its carapace, manifestly more nearly related to that species than to any other, have suggested to us some corrections in this careful restoration which have already been dealt with in the preceding generic discussion. The
 Figure 65 Ventral appendages of Stylonurus excelsior Hall. C, chelicera; B, one of first pair of endognathites; D, G, coxae of legs of second and third pair. Natural size. (From Hall & Clarke) |
Another alteration of the restoration of S. excelsior, suggested by evidence afforded by S. cestrotus, relates to the structure of the eyes. The carapace of Beecher's restoration is a cast from the Rutgers College specimen. In this the eye regions 
Figure 66 The terminal portion of the median dorsal ridge of Stylonurus excelsior, showing the ocelli. Natural size. (From Hall & Clarke) exhibit an inner circular depression described by Hall and Clarke as the eye. This is encircled on its outer edge by a conspicuous subsemicircular orbital ridge, but separated from the latter by a concentric level area bearing the same sculpture as the rest of the carapace. In much compressed or collapsed carapaces of S. cestrotus the eye presents an aspect very like that of this specimen of S. excelsior. In a few better preserved examples however [pl. 49, fig. 1,] the eye is highly prominent, looking like a bean lying on the carapace and the large semilunate visual surface surrounds a small, subcircular top area [pl. 50, fig. 1]. The logical inference hence is that the visual node of S. excelsior bulged in the same way and we have represented it thus in our restoration. The intense concentric wrinkling of the area within the orbital ridge in the specimen in the National Museum is direct evidence of the collapse of the visual node.
By analogy it would be necessary to infer that the central circular broken area in the eye of S. excelsior is the outer end of the palpebral lobe and the entire surrounding concentric area the visual surface. The latter part of this inference is at once invalidated by the fact of the extension of the surface sculpture upon the concentric area. The first part of the inference that the broken down inner circular areas were parts of the palpebral lobes is supported by the fact that in the National Museum specimen this part projects prominently; further in all other species of Stylonurus the visual surface is a more or less narrow crescent on a circular base [see S. megalops, S. myops and S. scoticus], and it therefore should not be assumed to be circular in S. excelsior.
Some closer study of the eye region in the two carapaces of S. excelsior has furnished the solution of these apparently contradictory facts in the finding of distinct, narrow crescentic, visual areas on the outside of the broken, circular, palpebral area. They are particularly well seen in the Rutgers College specimen, where they are clearly outlined although somewhat obscured by having become infolded at the collapse of the visual node.
We picture, then, the original aspect of the eye of Stylonurus excelsior as a bulging subhemispheric, visual node, supported on the outside by the strong orbital ridge, on the inside by the median ridge of the carapace and the transverse palpebral lobes. At the apex of this node and at the outer end of the palpebral lobe the relatively small crescentic visual surface was situated.
It is obvious that the visual area did not keep step with the growth of the carapace and of the visual node and thus became finally a relatively small band around the apex of a high node. This giant merostome would thus seem to have possessed very small eyes in comparison with smaller eurypterids, a feature common in the giants of other groups, as in the whales and elephants among the mammals.
Stylonurus? limbatus nov.
The collections from Schenectady and Duanesburg contain half a dozen specimens that are strikingly different from the associated eurypterids in greater relative length of carapace, broad, flat margin and subcentral position of the rather close-set large circular eyes, or eye nodes. All these characteristics suggest the generic reference of this interesting species to Stylonurus. The presence of this genus, or rather of that branch of the eurypterids which leads to the late Siluric and Devonic Stylonurus, is further indicated by body segments (tergites) [pl. 85, fig. 6] which have the form and ornamentation of the Otisville species Stylonurus myops.
Description. Carapace elongate semielliptic, a little longer than wide, widest at the base and contracting uniformly to the front which is evenly rounded. The posterior margin is straight transverse. The carapace is surrounded on all sides by a distinct border which is broadest in front where it attains one eighth the length of the carapace, and narrowest along the posterior margin. On the upperside this border slopes outward and is smooth, on the underside it was flat and concentrically grooved. The eye nodes are large, about one fifth the length of the body, circular, situated just in front of the transverse middle line of the carapace, close-set, about their own diameter apart. The visual surface has not been clearly distinguished from the node and it may have occupied the entire node. The ocelli have not been seen. The ornamentation is not visible on the carapace, but tergites probably belonging to the same species show circular to elliptic, relatively large nodes.
The tergites are strongly curved, convex forward in the middle and concave toward the sides, with very prominent "ears" at the antelateral angles and much rounded postlateral angles. They were very convex in the middle and surrounded by a depressed border.
Long slender tubular leg segments [pl. 85, fig. 9] and broad flat leg spines also occur in the Frankfort shale, such as among the later eurypterids are only known from the Stylonurus group.
Horizon and localities. Frankfort shale (Schenectady facies) at Schenectady and Duanesburg.
Remarks. Besides these elongate carapaces, a broad short carapace with the eyes far apart has been found at Schenectady [pl. 85, fig. 4]. This closely resembles the S. myops from Otisville. Like the latter, it has a very broad, concentrically striated or grooved border. This carapace quite probably represents a distinct species; on account of the rather unsatisfactory preservation of the single carapace representing it, we have refrained from naming it.
S. limbatus was of fairly large size. The carapace selected as type is 38 mm wide and 39 mm long.
Stylonurus (Ctenopterus) multispinosus nov.
Unknown Eurypterid (genus?) Sarle. N. Y. State Palaeontologist Rep't. 1902. p. 1105, pl. 26, fig. 2–4
Mr Sarle collected from the Pittsford shale a group of endognathites that present characters quite different from those of the associated species. He gave an elaborate description of the fragments but was unable to refer them to any of the genera of eurypterids and therefore suggested that "with more perfect material the forms will be found to represent a new genus."
Our entire specimen of Stylonurus cestrotus from Otisville furnishes the clue to these organs, in showing that the longest endognathite of the group corresponds to the third pair in Stylonurus, subgenus Ctenopterus. The general form and the relative dimensions of the parts of this endognathite are quite precisely those of Stylonurus. We infer from these facts that the fragments indicate the presence of a fairly large species of Stylonurus in the Pittsford shale. As this form is recognizable from the figured parts, we venture to name it.
Sarle's description of the fragments is as follows:
An eurypterid differing very materially from anything described from the Bertie waterlime, is represented in the collection by a group of four incomplete arms and a body segment, and by another of two incomplete arms.
In the first group [pl. 50, fig. 10] the longest of the arms has the coxal and succeeding five joints preserved. These are long, measuring altogether 110 mm in length. The three distal bear a series of long, curved spines. The form of the coxal joint is subtrapezoidal, the anterior side being considerably the longer. The breadth and the mean length are each about 18 mm. The dentate border is slightly produced and in length is equal to about one half the breadth of the joint. The dentation begins at the front end with an isolated, blunt tooth pointing forward, followed by sharp, curved teeth of small size which grade posteriorly into fine, hairlike bristles. The anterior side of each joint from the second to the sixth inclusive, is arcuate. The posterior sides of the second and third joints are straight, of the fourth, fifth and sixth, concave. The distal end of each is at right angles to the long axis. The second joint is narrower (14.5 mm) than long (23 mm); the third just twice as long (28 mm) as wide (14 mm); the fourth a little longer than the preceding (30 mm) and less than half as wide (7 mm). Along the concave, posterior side of the fourth are articulated five, long, curved, striated spines, nearly perpendicular to the joint. At the distal end of the series there is an indication of another. The most complete of these spines is 16 mm in length. The fifth joint is 16 mm long and 6 mm wide. Near the anterior end of the posterior edge it carries the stump of a large spine followed by the sockets of four more. The sixth joint bears the basal portion of three spines, but is so crushed and foreshortened that neither the original number of spines nor the length of the joint can be determined. Judging by the taper of this arm, there may have been two more joints.
The remnant of another appendage appears to be part of the proximal four joints, and measures 32 mm in length. From its robustness, it seems to have belonged just in front of the last mentioned. The peculiarities of these joints are their shortness and their thickening at the articulations. The joint, which on the tablet lies nearest to the large arm, is a little inflated and, though very imperfect, has the appearance of being the coxal joint.
The two other appendages of this group are robust and short. One is tolerably complete, apparently lacking only the dentate border of the coxal joint. It is 38 mm long and consists of seven joints. The coxa is large and globose. Each joint from the second to the fifth carries on the posterior edge a pair of short, stout, distally directed, lanceolate spines, averaging 2.5 mm long and nearly half as wide. Joint two is broad and very short. Joints three, four and five are subquadrate and successively smaller. Joint six is nearly one and one half times as long as broad and at the end bears two distally directed spines, one anterior, the other posterior. The seventh is long and clawlike, slightly inflated at the base. The other appendage is so crushed and folded that little can be determined by it. However, from the larger size of the coxal joint, it is probable that its position on the body was behind the more complete. The spines preserved on it, like those of the smaller appendage, are short and lanceolate.
The body plate in this group is very narrow (76 mm) as compared to its length (23 mm). Its division into right and left halves by a suture, the arching of each half and the produced antelateral angles indicate it to have been a paired sternite.
In the second group one of the imperfect arms consists of the four distal joints, the other of two imperfect proximal joints. The joints of the former are short and expanded at the articulations. The first and second are each provided on the posterior side with a pair of distally directed spines. These are long, curved and sharp like those of the large arm of the other group. The second has also, on the opposite side of the distal angle, a single, large one extending parallel with the axis of the arm. The penultimate is long and shows no sign of having been spiniferous. The terminal is about equal in length to the spines and, like the terminal appendage in the other group, is clawlike. This arm, judging from the shortness of the joints and the broadening at the articulations, probably corresponds to the second described from the other group. The joints of the other arm appear to correspond to part of joints two and three of the first of that group.
Associated with this last, and lying partially beneath its larger end, is a fragment of test which is ornamented by sharp, triangular scales differing from anything found on the other eurypterids herein described. However, it is not certain that this had any connection with this arm. Aside from this possibility, neither the appendages nor the sternite show any signs of ornamentation.
The most noticeable features revealed by these specimens are: the robustness and the great difference in size of the several pairs of endognathites; on the anterior three of these the arrangement in pairs of the posterior spines, which, on the first two, are noticeable for their shortness and lanceolate form, and on the third for their length and curvature; the high degree of specialization of the fourth pair of endognathites, shown by the great length of the joints and the number and large size of the spines; the narrowness and proportionately great length of the compound sternite; and the probability of there being several compound sternites. It is evident that the animal had a long, slender body with long, very strong limbs.
From a comparison of these parts with those of the various genera of eurypterids, it appears that they do not agree very closely with any. To show this, it is necessary only to point out certain of the more evident differences. In Eurypterus proper the fourth endognathite, to which I consider the longer of these arms to correspond, consists of nine joints, probably a greater number than is possessed by the other; besides, it bears no spines except the two formed by the prolongation of the eighth or penultimate joint. On the three anterior pairs of endognathites the spines are more uniform in shape and size. The body is proportionately broader and shorter than that indicated by the sternite described above. In eurypterids of the type of Eusarcus scorpionis Grote and Pitt, Carcinosoma newlini Claypole, Echinognathus clevelandi Walcott, Eurypterus punctatus Salter, E. scorpioides Woodward, E. scoticus Laurie, etc., so far as material shows, the preabdomen is obese, the second pair of endognathites is the longest, and all four pairs with their spines are curved forward. In Stylonurus and the related genus, Drepanopterus, the fourth endognathites are without any elaborate development of spines, and in the former are greatly elongated. In Slimonia the first pair of endognathites is tactile, the succeeding three pairs are short, vary little in size and are all provided with small spines at the distal ends of the joints. In the Pterygotus the four pairs of endognathites are filiform, of nearly equal size and probably in all cases, spineless.
A metastoma of peculiar form, figured by Sarle [op. cit. pl. 12, fig. 5; here pl. 46, fig. 15] and referred to in the explanation of his plate as "Dolichopterus?? metastoma of an undetermined form," approaches in shape more closely the metastoma of Stylonurus than that of any other genus. It seems to us very probable that it also belongs to this species.
Stylonurus myops Clarke
Eurypterus myops Clarke. N. Y. State Mus. Bul. 107. 1907. p. 306, pl. 6, fig. 1–5
Eurypterus maria Clarke. Ibid. pl. 3, fig. 6
Eurypterus or Pterygotus. Ibid. pl. 6, fig. 8
Segments and joints of Eurypterus, Hughmilleria, etc. Ibid. pl. 8, fig. 4
In the preliminary note on the Otisville fauna this species was considered as being "in many respects a diminutive expression of Eurypterus pittsfordensis Sarle, the head (all that is now known of it) being subquadrate, almost as much squared in front as behind, the eyes large, semicircular, subcentral and approximate and the ocellar mound developed in mature forms." The greatly enlarged collections from the same locality secured by the State Museum since the date of the preliminary paper, throw a different light on the generic relations of this species, and furnish the data for the following description.
Description. Carapace subrectangular, its length and width approximately as 2 : 3; both the anterior and posterior angles approaching right angles in older specimens; anterior angles, however, more rounded than the posterior ones. Frontal margin varying in different specimens from slightly convex to gently emarginate; lateral margins moderately convex, posterior margin broadly concave. The greatest width is found in the middle between the anterior and posterior margins. The upper test carries but a very narrow thickened rim on the anterior and lateral margins; it is continued, however, into a very broad, concentrically furrowed doublure on the underside, which in front attains one sixth the length of the carapace and becomes reduced to one half that width toward the genal angles. The eyes are very large (one third of length of carapace); much elevated, furnished with a semicircular, narrow visual area; approximate, about their own length apart, situated a little forward of the bisecting line. The ocelli are situated on a prominent, heart-shaped mound between the posterior extremities of the lateral eyes. The surface is covered with closely arranged prominent tubercles which along the frontal margin are arranged in concentric rows.
The first tergite is short and wide and like the following furnished with a row of large tubercles along the posterior margin.
| Measurements of type [first specimen figured, 1907, pl. 6, fig. 1]. | millimeters | |
| Length of carapace | 12.3 | |
| Width | 16.5 | |
| Width of doublure | 1.5+ | |
| Length of lateral eye | 2.5 | |
| Distance between visual surfaces | 9. | |
| Exposed length of first tergite | 1.2 | |
| Width | 12.4 | |
| The smallest carapace observed measured | ||
| Length of carapace | 3.5 | |
| Width | 5.5 | |
| Length of lateral eye | .9 | |
| Distance between visual surfaces | 4. | |
| The largest carapace observed measured | millimeters | |
| Length of carapace | 19. | |
| Width | 27. | |
| Length of lateral eye | 6.9 | |
| Distance between visual surfaces | 12.8 | |
Horizon and locality. One of the rarer forms in the Shawangunk grit at Otisville, N. Y.
Remarks. The principal features which characterize this species as belonging to Stylonurus are the broad, furrowed doublure, the large size of the eyes, the semicircular outline of the visual surfaces and their approximate position and the rows of tubercles along the posterior margins of the tergites. In the general outline of the carapace and its relative dimensions S. myops may be compared to S. powriei, megalops and scoticus. The great size of its eyes recalls S. megalops and, as in that little known Scottish form, the visual surface extends over more than a semicircle. Its prominent ornamentation distinguishes it from all of these species.
The later collections from Otisville have afforded some carapaces [pl. 51, figs. 8–12] of very young individuals (width but 5 mm) which differ so much from that of the mature type that they would be easily taken as representing a different species. They are broader and shorter and semicircular to semielliptic in outline. The lateral eyes are close to the margin instead of approximate; and their visual surface is relatively less extensive. The entire surface is so densely covered with tubercles that it has a shagreen aspect. Most of these ontogenetic characters are probably of phylogenetic importance, especially the change in the form of the carapace and in the position of the eyes. These have been noted more fully in another place.
A number of specimens [pl. 51, fig. 14; pl. 52, fig. 9] exhibit a distinct acute process in the middle of the frontal doublure. The same specimens are also relatively a little shorter. For this reason we consider it possible that both these features are due to a slight lateral compression, which undoubtedly has affected the specimen, figure 9. Larger collections may, however, bring out the fact that we have here to deal with varietal differences.
Besides the carapaces and attached first tergites, fragments of other parts of the test of a Stylonurus occur at Otisville and their prominent rows of tubercles suggest that they belong to this species. Most easily recognized among these are the tergites [pl. 53, fig. 4, 5]. Besides the posterior row of tubercles borne on a high crest, these show a parallel middle row of less distinct tubercles, which also crown a narrow ridge. In some a row of smaller and less distinct tubercles is seen posteriorly of the other and alternating with it. Further, densely tubercled metastomas of the shape of that reproduced on plate 53, figure 1 occur not infrequently. They probably also belong to this species. Portions of legs with longitudinal rows of tubercles [fig. 7] suggesting their reference to this species, have also been observed.
A single entire individual has been observed and, judging from the subrectangular outline of its carapace and the size and position of the eyes this probably represents S. myops [pl. 52, fig. 6]. Unfortunately its test is reduced to a film that retains no sculpturing and shows nothing but the outline. The most characteristic features of the specimen are its relatively compact form and the small length and great width of the abdomen and the long spurlike epimera of the segments, both of the preabdomen and postabdomen. The total length of the specimen is but 55 mm, its greatest width however amounts to 20 mm.
Such spurlike epimera of equal relative size are possessed only by the large S. scoticus from the Old Red sandstone. Curiously enough that isolated and strange form is like S. myops in outline of carapace, the approximate position of the eyes and the sculpture of the tergites. It seems probable therefore that S. myops, when fully known, will prove a representative of the subgenus Tarsopterus of which S. scoticus is the type.
Of the telson of the species, but a small proximal portion is preserved.
Ontogeny of Stylonurus myops
Among the early stages of eurypterids obtained at Otisville is a number of very minute individuals, that are noticeable for their owllike appearance due to the very broad, anteriorly emarginate carapace and their immense hemispherical and disklike eyes [pl. 51, figs. 1–6]. Although there is a considerable gap in size in the series of these specimens and of the smallest of the carapaces [pl. 51, figs. 7–9] which undoubtedly belong to S. myops, these small entire individuals seem properly referred here, for the following reasons: The form of the carapace is clearly that of S. myops which is the only one in the Otisville fauna possessing a subrectangular outline; the position of the eyes corresponds to that found in the adult stages of S. myops; the broad rim of the carapace, a characteristic feature of S. myops and not observed in other members of this fauna, is present in these young individuals.
In surveying this whole series, one distinguishes three ontogenetic groups, the first represented by the small entire individuals on plate 51, figures 1–6; the second by the group plate 51, figures 7–14, and the last by the specimens plate 52, figures 1–4, 10. As the smallest specimens of the first group are but little larger than the eggs of Limulus and are thoroughly larval in their character, we consider them as representing the nepionic stage. The next group which is intermediate in its character between the first and last may be considered as representing the neanic growth stage, since the last group belongs to specimens of ephebic or mature age, as far as we can judge, although we suspect that these are only the earliest ephebic substage.
The nepionic stage is again subdivisible as far as our material is concerned, into two substages. The first of these, illustrated by the figures 1–3, [plate 51] is characterized by (1) the relatively large size of the carapace to the body (proportion as 1 : 3.75 in the former and as 1 : 5 in the latter); (2) the evenly terete or conical form of the body which makes the carapace also the broadest part of the integument; (3) the presence of a distinct border surrounding the whole carapace; (4) the immense size of the eyes, which occupy the entire space between the border and a median ridge; (5) this distinct median ridge, also a character not observed in later stages, and finally the abdominal segments which are (6) less in number and (7) lack all differentiation between preabdomen and postabdomen as far as the length of the segments is concerned, all being of equal length.
We may now consider some of these larval characters in somewhat greater detail.
The carapace appears to have had more distinctly the nature of a definite shield than at any later stage, for it is here most clearly set off by a flat thickened border of equal width. The same impression is also conveyed by the rounded postlateral angles, well seen in figures 1 and 3.[30]
The large size of the carapace, its distinction from the abdomen and the broad border, are features which this larva has in common with Limulus [text fig. 24], with the difference, however, that in the latter the border is not continuous over the posterior margin. But there are still other features inviting comparison with the larva of Limulus, notably the median ridge, which produces a trilobation of the carapace directly corresponding to that of Limulus in the so called "trilobite stage." It further appears that the number of segments of the abdomen may be the same as that observed in the larva of Limulus shortly after hatching, that is nine including the rudiment of the caudal spine. Eight (including the telson) are distinctly visible in the original of plate 51, figure 4, but it is probable that the first segment is hidden under the carapace. As in the larva of Limulus these segments are not differentiated, at least in their dorsal view and the telson spine is still extremely rudimentary. But herewith all similarities end.
The uniformly terete form of the abdomen of this larva is in strong contrast to the broad, posteriorly widening abdomen of the Limulus larva. There is little doubt that the latter represents a tachygenetic character of later acquisition and that S. myops exhibits the more primitive condition.
Another striking feature of this nepionic form not seen in the larva of Limulus is the great size of the lateral eyes which suggests very strongly the megalops stage in the zoea of many crustaceans. The large eyes appear in most specimens as disks bearing a central node [pl. 51, figs. 1, 5]; in some as globose projections with an apical depression [pl. 51, fig. 2]. By tracing these parts through later stages to the adult form, it becomes apparent that the disks or semiglobes are the large visual nodes with an outer orbital ridge and that the apical nodes are composed of the crescentic visual surface[31] and the included apical area as in the mature S. excelsior. With this conception of the parts of the eye, it follows that the visual node was protruded enormously as in the megalops stages of the crustacean larvae. This protrusion disappears entirely, as figures 7–13 show, and only the small visual node surrounded by the visual surface on the outer side remains. In figure 5 the outer orbital ridge is still very well seen; in figure 6 it seems to have merged into the semilunar ridge that runs parallel to the anterior and lateral margins of the carapace.
The original position of the visual surfaces, or eyes proper, in the earliest larvae seems to have been about halfway between the anterior and posterior, margins and nearer to the lateral margin or border than to the median ridge. This position is retained throughout the neanic stages. It is identical with that observed in the larval Limulus. With the beginning of the ephebic stage the compound eyes wander inward and become approximate [as in pl. 52 fig. 1–4] and thereby assume the position characteristic to most species of Stylonurus.
The neanic and ephebic stages exhibit a strong tubercular ornamentation of the carapace and segments. No indications of this have been observed in the nepionic stage, a fact that may be attributed either to a failure to observe it on account of the extreme smallness of the specimens or to its absence. We believe the latter to be the case for several reasons. One of these is that the largest specimens of the nepionic stage [figs. 5, 6] could have hardly failed to show traces of this sculpture if it existed, and another, that the smallest carapace of the neanic stage observed [fig. 8] possesses this tubercular sculpture only in an incomplete or but partially developed form. Moreover, the fact of the absence of the ornamentation of the mature forms in the larvae is fully in accordance with the relations of the larvae and mature forms in most other arthropods.
The neanic stage, typically represented by figures 7–13, is distinguished from the ephebic stage mainly by two characters, the relatively greater width of the carapace and the submarginal position of the compound eyes. In the carapaces, plate 51, figures 9, 11, 12,[32] the average relation of length to width is as 10 : 16[33] and in plate 52, figures 1–3, as 10 : 14.[34]
Actually the relative length of the carapace increases but little (about one eighth) with advancing age but the fact that in the neanic stage the anterior angles of the carapace are strongly truncated and rounded and in the mature stage subrectangular, assists greatly in increasing the appearance of smaller length and greater width in the neanic specimens. Specimen figure 14 which has almost the size of the mature specimens, still retains the neanic position of the eyes and the round anterior angles and stands in the proportion of length to width between the neanic and nepionic stages as 10 : 15.
The submarginal position of the compound eyes in the neanic stage is a feature inherited from the preceding stage and corresponding to the appearance of these eyes in the larva of Limulus at the line of insertion of the rimlike edge of the lateral lobes [text fig. 24]. A peculiar difference, apparently at variance with the enormously enlarged eyes in the larval condition between the neanic and ephebic stages consists in the relatively smaller size of the visual surface and inclosed node in the former [cf. fig. 9, 11 with pl. 52, fig. 2, 3][35]. But if, as we have inferred before, the final visual node and visual surface in the nepionic stage are represented by the central or apical node borne on the large larval visual node, then the small size of the eye in the neanic stage is the direct result of the nepionic condition. We have then the peculiar fact, that in the ontogeny of S. myops the actual visual surface of the eye increases relatively with advancing age, while the visual node on which it is borne, greatly decreases.
The ocelli have not been located in the nepionic stage, but their position midway between the lateral eyes in the neanic stage can be clearly made out.
In tabular form the character of the three stages and the changes are as follows:
| Nepionic Stage | Neanic Stage | Ephebic Stage | ||
| Carapace | 
|
Large | Decreases in relative size | Continued decrease |
|
With broad border | Border becomes narrower | Border more or less narrow and obscure | |
| Compound eyes | 
|
With immense visual node | Visual node small | Visual node small |
|
Position submarginal | Submarginal | Subcentral | |
|
Visual surface relatively small | Visual surface relatively small | Visual surface relatively large | |
| Abdomen |
|
Segments 7–8 | Unknown | 12 |
|
|
No distinct differentiation | Distinct differentiation | ||
| Preabdomen | Regularly narrowing posteriorly | Widest at fourth and fifth segments | ||
| Postabdomen |
|
No epimera | Long epimera | |
|
|
All segments equally long | Last segments much longer | ||
| Telson spine | Very short and blunt | Long and slender (?) | ||
| Sculpture | None | Tubercles | Tubercles | |
Stylonurus beecheri (Hall)
(Text figure 67)
Eurypterus beecheri Hall. 2d Geol. Sur. Penn. Rep't PPP. 1884. p. 30, pl. 3, fig. 1
Eurypterus beecheri Hall & Clarke. Palaeontology of New York. 1888. 7: 157, pl. 27, fig. 5
Stylonurus beecheri Beecher. American Journal of Science. 1900. 10:148
We have nothing to add to the elaborate original description of this form, since no other specimens than the holotype are known. As the
Figure 67 Stylonurus beecheri (Hall). Figure of original specimen. Natural size. (From Hall & Clarke)
The specimen serves to demonstrate the persistence of the genus Stylonurus into late Devonic time, the type coming from the Chemung sandstones at Warren, Warren co., Penn.
Stylonurus (?) wrightianus (Dawson)
(Text figure 68)
Equisetides wrightiana Dawson. Quar. Jour. Geol. Soc. 1881. 37:301, pl. 12, fig. 10; pl. 13, fig. 20
Equisetides wrightiana Wright. N. Y. State Mus. Nat. Hist. 35th Rep't. 1884. p. 196
Stylonurus (?) wrightiana Hall. Ibid. pl. 15, note
Echinocaris wrightiana Jones & Woodward. Geol. Mag. 1884. Dec. 3; 1: 9; p. 393, pl. 13, fig. 1, a, b
Echinocaris wrightiana Etheridge, Woodward & Jones. 3d Rep't Committee on Fossil Phyllopoda of the Palaeozoic Rocks. 1885. p. 35
Stylonurus (?) (Echinocaris?) wrightianus Hall & Clarke. Palaeontology of New York. 1888. 7: 160, pl. 27, fig. 7–9
Stylonurus (?) wrightianus Beecher. American Journal of Science. 1900. 10: 148
The foregoing synonymy reveals the interesting history of a two jointed subcylindrical fragment from the lower beds of the Portage sandstones, Italy, Yates co., N. Y. Originally regarded as of vegetable nature, Hall early recognized that its surface sculpture was that of an arthropod and that it probably represents "two of the abdominal segments of a form not unlike Stylonurus." Woodward and Jones then referred the fragment to the Phyllocarida (Echinocaris), evidently basing their opinion on the spinose character of the surface of the fragment. Hall and Clarke later pointed out that no species of that genus possess spines of similar character to those in the specimen and that the latter would be gigantic for Echinocaris but not for a species of Stylonurus. Finally Beecher suggested that the specimen represents two proximal segments of one of the large crawling legs of a form related to Stylonurus, and not two somites of the abdomen as indicated by Hall, claiming that "its elliptical or ovoid sections without any flattening of the epimera, the very considerable overlapping of the joints, and the configuration of the suture, are
 Figure 68 Stylonurus? wrightianus (Dawson). Dorsal and lateral views of the original specimen, and enlargement of surface. (From Hall & Clarke) |
more strongly indicative of the nature and requirements of a limb than of abdominal segments." The entire specimen of Stylonurus obtained at Otisville would seem to corroborate the latter view.
Stylonurus sp. α, β, γ, δ.
Besides the fairly complete species of Stylonurus (S. cestrotus and S. myops) which the shales of the Shawangunk grit at Otisville have afforded, fragmentary remains indicate the presence of several other representatives of the same genus, which for the sake of completeness, may be mentioned in this place.
α. Plate 53, figures 8, 10–12. One of these is characterized by its acutely triangular scales, which assume the aspect of short sharp spines and actually seem to have consisted of such in the specimen, figure 10, where the fact that the distal parts of the scales are always broken off, is evidence of their spinose nature. The fragments of segments indicate that these possessed distinct anterior and posterior borders. A single segment of one of the first or second pairs of legs has been obtained. This by its lateral row of spines permits a reference of the species to the subgenus Ctenopterus.
β. Plate 53, figures 14, 15. A second species, quite probably also referable to Ctenopterus, is best represented by the leg segment reproduced in figure 15. This shows a series of teethlike serrations, quite dissimilar to the rows of spines in other species.
γ. Plate 53, figure 19. A third leg segment, also possessing the characteristics of Ctenopterus, shows broad, flat (paired?) spines with longitudinal striae; these features strongly reminding one of the leg spines of S. excelsior.
δ. Plate 53, figures 6, 9. Some patches of integument bear a sculpturing which consists of flat, broad, distinctly separated prominences and in part of long ridges, the whole resembling a cobblestone pavement. This is so strikingly different from all other ornamentation observed in the beds at Otisville, that it can not fail to characterize its possessor. It is more suggestive of the ornamentation exhibited by such forms as S. excelsior, scoticus and myops than of members of other genera.
Some other specifically indeterminable fragments deserving mention, may be noted here. One of these is the distal portion of one of the posterior legs [pl. 53, fig. 20] of a Stylonurus, chiefly remarkable for its size, indicating the presence of large individuals of the genus in this Otisville fauna. Another fragment of a segment [pl. 53, fig. 13] exhibits a curiously serrated posterior margin. This recalls the frontal serrations of the carapace of S. cestrotus, but the segments of that species have not shown this structure, although on account of their rather poor preservation, this does not yet demonstrate the absence of this fringe. We are not certain that this specimen is referable to Stylonurus.
To a gigantic Stylonurus or Pterygotus probably should also be referred two fragments of plates with marginal rows of slightly curved, rather blunt spines [pl. 53, fig. 16, 17]. These are apparently portions of the manducatory edges of coxal segments. In the smaller specimen the teeth are very thick and solid, in the second they are so much wrinkled and shrunken that they give the impression of having been hollow processes. It is possible that these remains require an entirely different explanation, but the material is at present too fragmentary to permit of positive conclusions. There is a suggestion of similarity between these peculiar fringed bodies and the supposed combs of giant scorpions such as have been described by Peach as Glyptoscorpius, both the fringe and the parallel lines of the base of the fragments indicating the structure seen in the rhachis and the comb of certain recent scorpions. With present knowledge the comparison can be carried no further.
Subgenus DREPANOPTERUS Laurie
In 1892 Laurie created a new genus for a single, then rather incompletely known eurypterid, from the Siluric rocks of the Pentland hills in Scotland. He defines the genus as follows:
Carapace broader than long; widest about two fifths from anterior margin. Body, 1st segment wider than posterior margin of carapace; increases in width to 3d segment, and then tapers rapidly. Limb elongated, subcylindrical, terminating in a very slightly expanded joint, concave on posterior margin.
The subsequent discovery of two other species and of better specimens of the genotype led Laurie [1899, p. 582] to consider the point of chief generic importance to be a negative one: "Last pair of appendages
 Figure 69 Drepanopterus pentlandicus Laurie. Original figure. (From Laurie) |
Laurie [1893, p. 519] suggests that "the form of the two last pairs of legs [of Stylonurus], which are long and pointed at the end, and are among the most characteristic structures of the genus, is possibly derived from Eurypterus through some form like Drepanopterus, though it is also possible that Stylonurus is descended from an ancestral type in which the last pair of legs were less modified than in Eurypterus." In view of the early appearance of Drepanopterus, and the fact that the young of D. longicaudatus show no indication of eurypteroid features in their limbs, we are convinced that the last of the alternative hypotheses of Laurie is nearer the truth and that Stylonurus is not derived from Eurypterus but comes through Drepanopterus from a like ancestor with Eurypterus.
Drepanopterus longicaudatus nov.
Plate 25, figure 3; plates 54–56
Description. Body slender, of medium size, clavate in general outline, the carapace being broadest and the body tapering to the long telson.
The carapace is subquadrate in a young specimen, but an ephebic individual has the sides so well rounded that it appears subcircular, with the posterior parts contracted. In the young specimen, the length is to the width as 7 : 8, in the ephebic example, as 8 : 9. It is widest in the middle portion and contracts again by about one seventh of its width toward the base. The doublure is about 3 mm wide in the type specimen and relatively wider in the young. It diminishes in width posteriorly and finally runs out. The margin of the carapace is bounded by a thickened border, behind which several parallel striae are observed. The eyes are somewhat indistinct in the specimens; they appear to have been large and consisted of almost circular visual surfaces surrounding circular prominences. The latter occupied one fifth of the length of the carapace, were situated on the anterior half and not quite twice their width asunder. The ocelli have not been seen. The preabdomen is relatively very short (its length amounting to only two thirds that of the carapace) and broad (proportion of length to width as 4 : 5), its greatest width being attained in the region of the fourth tergite whence it contracts rather rapidly. At the widest part of the preabdomen, the tergites seem to be about six and one half times as wide as long. Their general form is but indistinctly discernible in the carbonaceous film, but seems to have been that of straight transverse bands. The operculum is not appreciably wider than the other sternites and the next sternite fully as wide. The details of the outlines of these and the following sternites have not been made out. The third sternite (the widest) is, in its exposed or not overlapping part, eight times as wide as long. The posterior margins are uniformly concave, the curvature increasing in the succeeding segments. The median suture is well seen in a young specimen [pl. 25, fig. 3]. The postabdomen shows an immense development; it is nearly as long as the carapace and preabdomen together and occupies about one third of the total length of the body. The first postabdominal segment still corresponds in anterior width to the preabdomen, but it contracts so rapidly that its posterior margin is shorter by one fifth and the final width of the postabdomen is but one third of that at its beginning. While thus the postabdominal segments diminish greatly in width posteriorly, they increase in a still more striking manner in length, for the last segment is nearly four times as long as wide; the postabdominal segments thus change from short, wide rings to relatively long, narrow tubes, the last three being the most markedly subconical. The posterior doublures, about 4 mm wide, are well seen on plate 55. There are keels parallel and near to the lateral margins of the postabdominal segments. The telson is enormously developed. It not only occupies nearly one third of the length of the whole body, but is also very strong and thick. In shape it is clavate, contracted at about one fourth of its length and expanding again, and reaches its greatest width at three fourths of its length. Its extremity is blunt.
Appendages. Of the postoral appendages of the cephalothorax, the third to fifth pairs of limbs have been observed in position and one of the preceding limbs has been seen detached [pl. 55]. The latter is of strikingly plump form, its greatest width being nearly one third of its length. Its segments are narrow rings, seven in number, increasing in width to the third and then gradually decreasing to the long, curved terminal claw. The last five segments bear each a pair of short, blunt spines. These, like the terminal spine, are longitudinally striated. This limb contrasts so much in shape with the third limb that we should be inclined to consider it, in view of the regular series which the third to fifth limbs form, as the first postoral appendage. But as Laurie has regarded a similar short, stout appendage as the second leg in Stylonurus macrophthalmus [1899, pl. 1, fig. 4] and as the first limb of Stylonurus and Drepanopterus are practically unknown, we prefer to leave the question of the number of this leg open. The third limb is much longer, projecting with four and one half segments as much beyond the margin of the carapace as the base of the carapace is long. It is, however, not slender, its fourth joint being still two thirds as wide as long. The segments are tubular; each is narrower than the preceding, but widens again a little in the distal portion. Those exposed beyond the margin of the carapace bore two spines each at the distal articulation. The limb ends, like the others, in a terminal claw. The fourth limb is built on the same lines as that just described. It projects twice as far beyond the carapace with five segments exposed and these segments are, as in the preceding limb, of subequal length (except the fifth which is a little longer and the seventh which is much shorter) though greatly differing in width, the fourth being more than twice as wide as the last. The second and third segments can also be seen faintly outlined in specimen, plate 56. They are only about half as long as the following, but wider; the third is still much shorter than the second, as in other eurypterids, and forms a narrow ring. The undersides of the segments are furnished with two slender spines each. The next, last limb, is again almost twice as long as the fourth in its exposed portion and the slight differences in the lengths of the segments observed in the preceding legs are here greatly exaggerated, the second and third segments being narrow rings, while the fourth segment is greatly lengthened and the fifth again longer by one third. The next two segments (sixth and seventh) are each as long as the fourth, and the eighth is reduced to nearly half that length. The segments of this limb are not furnished with spines on the underside. The coxa of this limb is also outlined on plate 56. It is relatively small, its length amounting to not more than one third of the carapace; distinctly trapezoidal in outline, width and length are subequal, its anterior margin gently convex and larger by one fourth than the posterior. The manducatory edge was apparently short. The terminal claw of the last limb is as long as the last segment and curved inward.
The metastoma has not been seen.
Genital appendages. Specimen plate 56 shows a long elliptic impression, extending over the operculum and first sternite and suggesting a female opercular appendage; and the young specimen on plate 25, figure 3, exhibits a short oval plate in the median line of the operculum.
Ornamentation. The surface sculpture shows a transverse row of sharply angular scales along the posterior margins of the segments on the upperside. Some of these along the median line of the postabdomen grew into distinct short spines. The remainder of the surface is covered with what look like smaller, more irregular, similar scales, the appearance of which may, however, be due to secondary changes in the substance of the integument, which gave it partly a scaly, partly a granular character. Some apparently well preserved portions of the integument are quite smooth.
Measurements. The type which is also the largest specimen, measures 295 mm. The carapace is 65 mm long and 73 mm wide at its widest part and 61.5 mm wide at the base. The eye had a longitudinal diameter of 13.5 mm. The preabdomen measures 42.5 mm in length and 61 mm in width; the postabdomen 96.6 mm in length and 53.5 mm at its beginning and 18 mm at its end. The length of the first postabdominal segment is 8 mm, that of the last 29 mm. The telson is 91 mm long and 7 mm wide. The third limb projects about 51 mm beyond the carapace, the fourth about 82 mm, the last about 135 mm. In a young specimen the total length is 93 mm, the carapace measures 21.5 × 24 mm, the preabdomen 18 × 22 mm, the postabdomen 31 × 16.5 mm (31 mm width at beginning and 6 mm width at end); the telson 23 mm. The fourth limb projects 26 mm, the last 44 mm.
Horizon and locality. Kokomo limestone of Kokomo, Indiana. Types (four specimens, nos. 12903 (holotype), 12904, 12908, 12911) in the University of Chicago collection.
Remarks. Drepanopterus longicaudatus is a unique form among the American eurypterids being the sole representative thus far found on this continent of this rare and phylogenetically interesting genus. From its Scottish allies, it is readily distinguished by its slender and elongated postabdomen and the long, clavate telson.
Two of the four specimens before us are only one third the size of the others, thus representing much younger stages. Nevertheless, their habitus and relative dimensions do not differ from those of the older as one might expect. This is especially obvious in the comparative lengths of the appendages and the telson to the whole body. In both the old and the young, the length of the last limb to that of the body is as 7 : 15 and that of the preceding limb to the last one as 3 : 5.
Genus ECHINOGNATHUS Walcott
This genus from the Lower Siluric of New York is based on unsatisfactory fragments which indicate relationship to Stylonurus and we associate them provisionally with that genus. Walcott's original diagnosis of Echinognathus follows [1882, p. 213]:
Endognathary limbs (one or more pairs) formed of eight or nine joints, six of which carry long, backward curving spines articulated to their posterior side. Terminal joint slender, elongate, acuminate. Surface of the body and larger joints of the cephalic appendage ornamented with scalelike markings, as in the genus Pterygotus. Type, E. clevelandi.
Two characters are not only the most prominent features of the originals[36] but also of distinct value in determining the taxonomic position of the genus. The first is the great number of paired long, flat spines to each segment of the endognathite. The common genera of eurypterids, as notably Eurypterus and Pterygotus, have but one pair of longer spines to each segment. The greater number of spines occur typically only in the genera Dolichopterus and Stylonurus, and but very exceptionally in other genera—the exceptions being Eurypterus dekayi Hall and probably also Eusarcus scoticus (Laurie).[37] Such continuous series of spines, however, as are exhibited by the endognathite of Echinognathus, are characteristic of the subgenus of Stylonurus here termed Ctenopterus.
It would also seem that the spines of Echinognathus possessed a rather flat, subtriangular section, giving them a bladelike appearance, a character which, coupled with a distinct longitudinal striation, is also repeated in certain species of Ctenopterus.
The second character that we have here in view, is the surface sculpture. This is also of unusual type and consists of very prominent oblong scales that rise rapidly behind and suggest raindrops running down a windowpane [pl. 58, figs. 1, 2], with a row of especially large drops at the bottom, on the posterior margin of the segments. This peculiar ornamentation is also best developed in species of Stylonurus, though it also occurs in some of the later, especially the Carbonic, species of Eurypterus.
Both the extreme spinosity of the endognathite and the surface sculpture indicate that Echinognathus, in comparison to Strabops or Eurypterus, was already a highly specialized genus and was either closely related to Stylonurus or had a convergent development to that genus as far as the two characters mentioned are concerned. There are no other characters observable in the fragments that would appear competent to shed light on its generic relations.
The monotype of this genus is
Echinognathus clevelandi Walcott
Plate 58, figures 1, 2
Eurypterus? clevelandi Walcott. American Journal of Science. 1882. 23: 152. figs. 1, 2
Echinognathus clevelandi Walcott: Idem. p. 213
We reproduce the original description as follows:
The only portion of the body discovered is illustrated by figure 1. It appears to be the left side or half of the ventral surface of the anterior thoracic segment. The reference to the ventral surface is from the presence of a thin membranous extension of the anterior margin, a feature observed on the anterior segment of Dolichopterus macrochirus Hall.[38] The test appears to have been thin and firm, and the margins are clearly outlined on the dark, smooth slate, while the surface is ornamented with fine scalelike markings on the anterior portion that increase in size toward the posterior margin (cc).
Figure 2 is a sketch, seven tenths of the natural size, of the cephalic appendage as it appears on the surface of the slate and in the matrix. The entire length of the appendage from the point a a to the end of the terminal joint seven, as restored to its natural position, would be 12.5 centimeters, exclusive of the basal joint at a a. The long spines of the joints 3 and 4 are 5 centimeters in length.
The joint marked (1) is broad and short with a rounded depression at the center of its inner margin. There is no evidence of the attachment of the long spines that are articulated to the posterior side of the succeeding joints. From the form of the joint and the presence of broken fragments of the test in the matrix at a a it is probable that it is the second joint of the appendage and that the first or basal joint is broken up. The joint (2) is large, elongate, rudely subtriangular, the long anterior margin curving around to meet the nearly straight posterior margin at its inner end. The latter margin has nine long curved spines articulated to it while the three following joints (3, 4 and 5) have but three each on their posterior margins. These joints (3, 4, 5), are more or less quadrangular in outline, (3) and (4) being transverse and (5) a little elongate. The spines of (3) and (4) are the longest of any attached to the appendage. Beyond (5) traces of another joint are shown (6), and another is indicated by the position of the three curved spines beyond those of (6). These two latter joints were crushed by the forcing back of the long terminal joint (7), the inner end of which is seen beneath the center of the joint (4). This joint or terminal spine is slender, slightly curved backward, and marked by a slight median ridge and longitudinal striae. The surface of the joint (1) and the anterior portions of (2) and (3) show the scalelike markings observed on the fragment of the thoracic segment. If there were but one joint beyond the transverse joint (1), i. e., the basal, the entire appendage would have had nine joints, if our interpretation of the crushed joints is correct.
The long curved spines (s, s, s), are a very curious feature of the appendage and the most marked character of the genus and species. They are articulated to the posterior margin of the joints, as the latter rest flattened out in the slate or shale, and there is no evidence but that they form a single series as shown in the specimen and in the drawing, figure 2. Each spine is constricted a little near its base, forming a rounded end or point of articulation; from this well out toward their pointed termination they retain an average width curving gently backward and inward. They appear to have been flattened when in a natural condition, and formed of a thin test which is rather strongly striated.
Horizon and locality. Utica slate, Holland Patent, Oneida co., N. Y.
Remarks. The great width of the earlier joints of the leg and the very rapid tapering of the limb suggest that it was a first endognathite and that it consisted of eight segments, counting the terminal spine. It is doubtful whether the spine that now holds a horizontal position, is the terminal spine, pushed far back, or only a lateral spine in an accidental position.
The fragment of a segment indicates by the strong rounding of the antelateral angles and the great length, that it might belong to an operculum, in which case the absence of a median transverse line would be remarkable; or to one of the first sternites. The crowding and the transversely elongate form of the scales in the anterior lateral region indicate that this part has been pushed together in posterior direction and the anterior margin is not complete. It probably extended as far forward as the median portion of the segment.
Mr Walcott has sent with the two types a third fragment which has not been figured hitherto, but which beautifully shows the character of the scales [pl. 58, fig. 2].
All the fragments and the size of the sculpturing indicate that Echinognathus clevelandi was a form of large dimensions and robust structure.
Genus MEGALOGRAPTUS Miller
Another eurypterid of the Lower Siluric is from the Richmond group of Ohio and was described by S. A. Miller [1874] as a graptolite under the name of Megalograptus welchi. When the junior author was engaged on the monograph of the Graptolites of New York, inquiry was made in regard to this curious fossil and the information obtained[39] through Drs Ulrich and Foerste that the species is based, as the figures at once suggest, on fragments of an eurypterid. Dr Foerste has been engaged for some time in an investigation of the Richmond faunas of the Ohio valley, and as he presumably had secured all the material available of this form, we have asked him to publish in this place that part of his manuscript referring to Megalograptus. To this request he has kindly acceded by sending the appended description. The photographs of Miller's types are here reproduced on plate 58.
Megalograptus welchi, S. A. Miller
By A. F. Foerste
Plate 58, figures 3–5
The Richmond group of Ohio, Indiana and Kentucky includes, in descending order, the following divisions:
| Elkhorn beds | Liberty beds |
| Whitewater beds | Waynesville beds |
| Saluda beds | Arnheim beds |
In Ohio, most of Indiana, and a part of northeastern Kentucky, the base of the Liberty bed is formed by a stratum in which the brachiopod Hebertella insculpta is very abundant. This stratum is overlain by one in which Plectambonites sericeus abounds, and at a still higher elevation Dinorthis subquadrata makes its first appearance.
The top of the Liberty bed is the horizon at which Gomphoceras eos, Gyroceras baeri, and several species of Cyrtoceras occur. Immediately below these cephalopoda, or associated in the same layers, a large form of Streptelasma rusticum is abundant.
The Liberty beds contain an interesting fauna. Ceraurus miseneri, Dalmanites breviceps, Brachiospongia tuberculata, and various crinoids occur here including Glyptocrinus richardsoni and Glyptocrinus fornshelli. The Liberty beds were a favorite collecting horizon for the crinoid hunters 40 years ago. It was while working out a pocket in which Dendrocrinus casei and Gaurocrinus onealli were abundant, that Megalograptus welchi was found. The locality occurs in the eastern edge of Warren county, Ohio. The road from Clarksville to Fort Ancient crosses Todds Fork half a mile west of Clarksville. A short distance beyond the point at which the road to Morrow turns off, on the left, is the home of Adam Pennington. The Megalograptus specimens were found about 100 yards directly west of the house, along a small stream. A wave-marked layer of limestone, 6 inches thick, overlies a few layers of limestone containing Dinorthis subquadrata. Farther down stream there are no exposures for about 25 feet, but it is evident from the stratigraphy worked out in the surrounding country, that the wave-marked layer here mentioned belongs about 15 feet above the Hebertella insculpta horizon. The Megalograptus occurred in a series of crinoid-bearing clays, 3 feet above the wavemarked limestone.
The specimens were discovered by Dr L. B. Welch, and the largest fragment, a nearly perfect endognathite, remained in his collection. A fragment of a second endognathite, and a large quadrangular fragment, regarded as the dorsal part of a postabdominal ring segment, passed into the possession of Mr S. A. Miller, by whom all three specimens were described and figured as Megalograptus welchi [Cincinnati Quar. Jour. Sci., 1874, 1:343]. The two specimens acquired by Mr Miller are now in the Walker Museum, at the University of Chicago. Other fragments have been found, but none of these give any additional information. It is probable that if at the time of discovery the fragments at hand had been recognized as that of some large eurypterid, much more could have been obtained. The collectors were after crinoids, and by the time that the black filmy fragments had been recognized as of interest, almost the entire specimen had been irretrievably destroyed.
The large endognathite belonging to the Welch collection was not thoroughly cleaned by Dr Welch, and I have taken great pains to determine its exact outline. In this, there has been fair success except in the case of the basal joint, where a part of the thin chitinous epidermal layer had already scaled off, and where the underlying rock offered no trace of an impression. In the case of the basal joint, therefore, the outline presented is that of the specimen in its present condition, and not of the perfect specimen. The specimen may be described as follows:
If that part of the specimen numbered 1A and 1B in the accompanying figure be the basal joint, then the masticatory edge does not preserve distinct serrulations. The posterior proximal corner is prolonged into a spinose projection. The posterior margin is not well preserved; at the distal end there is a minute denticulate projection. If the large segment here considered as a single basal joint in reality consists of two joints, as the reentrant angle both anteriorly and posteriorly seems to indicate, no trace of jointing could be found on the surface of the specimen.
The line of separation between the first and second joints is distinctly shown, but the distal corner along the posterior edge of the second joint is not well preserved, and its form, therefore, remains in doubt. Along the anterior margin of the second joint there are prominent spines. Of these, the spine nearest the distal margin is 15 mm long; a small spinose projection, 3 mm in length, appears to overlap the proximal end of the base of this spine. Opposite the middle of the second joint there is a pair of spines, apparently united for a short distance above their bases. The proximal edge of this pair overlaps, near the base, the distal edge of another spine, only 9 mm in length; and the latter, in turn overlaps a much greater part of still another spine, at least 6 mm long.
The distal corner of the posterior margin of the third, fourth, fifth and sixth joints is distinctly and acutely denticulate, and the lines between these joints are directly transverse.
Along the anterior margin of the third joint there are two conspicuous spines. Of these, the one nearest the distal end appears to be 17 mm long. In that case it would be the longest spine shown by the endognathite. At its base the proximal end of this spine slightly overlaps the base of a second spine, only 9 mm long.
Along the anterior margin of the fourth joint there are at least three spines. Of these, the distal spine is 10 mm, and the proximal one, 7 mm in length. The tip of the middle one is imperfectly preserved.
Along the anterior margin of the fifth joint there are at least two spines. Of these, the spine nearest the distal margin is 11 mm long, and the spine opposite the middle of the joint is 6 mm in length.
At the distal end of the anterior margin of the sixth joint, the epidermal skeleton appears prolonged into a spine 7.5 mm long and almost 4 mm wide at the base; the anterior edge of this spine appears to be in line with the anterior edge of the joint, so that the spine points toward the distal end of the endognathite instead of forming a considerable angle with the latter as in case of the spines on the preceding joints. The state of preservation of this spine is not satisfactory for accurate measurement. Possibly a second spine was attached along the line between the sixth and seventh joints near the posterior edge of the spine already described. As a matter of fact, little is known at present of the spines attached to this joint.
The seventh joint has a length of 15 mm and is divided along the middle by a deep notch so as to terminate in two spines 10 mm in length. It is possible that the structure described in the preceding paragraph as forming a spine belonging to the distal end of the sixth joint may in reality belong to the seventh joint, but this is not the interpretation made from the specimen in its present condition of preservation.
The overlapping shown by the bases of some of the spines shows that these were not arranged along a single plane, nor has it been possible to demonstrate a biserial arrangement. For the present, the more exact arrangement of the spines must be regarded as not definitely determined. The endognathite probably was distinctly flattened, as was suitable for an appendage of such large size in case of a swimming animal. As far as may be determined from the specimen at hand, the spines were arranged along the anterior face of the endognathite, and no spines have been found at any distance from this face.
The surface of the endognathite is ornamented by scalelike markings, which, toward the posterior border, become small although distinct. The raised border of these scalelike markings is nearest the distal end of the endognathite. The general distribution of these markings is unknown.
The second specimen, a fragment of an endognathite, which passed from the Miller collection into the Faber collection, and finally into the Walker Museum at Chicago University, probably is another fragment from the same individual. Judging from its size, it may represent the three joints preceding the terminal joint of one of the endognathites. In that case, the presence of the large spine and apparently also of a small spine along the distal margin of this fragment is noteworthy. As a matter of fact, the relative position of this fragment in the endognathite is unknown.
The third specimen, also formerly in the Miller collection, but now in the Faber collection in Walker Museum, is the dorsal side of one of the postabdominal segments. This position is indicated by its considerable length, compared with its width. The surface is ornamented by numerous scalelike markings, the raised border of which is directed toward the posterior extremity of the animal. Most of these markings are oval in form but along certain lines parallel to the length of the animal, they are more nearly oblong or linear in shape. These rows of linear scalelike markings unquestionably were more or less in line with similar rows on preceding and succeeding segments. Along these lines the segments were slightly elevated. These lines of scalelike markings and the slight elevations upon which they are found are at least four in number, and are separated by spaces 14 or 15 mm in width; they extend only along the posterior half of the segment at hand. Near the anterior extremities of these spaces, the surface of the segment is marked by irregular, shallow, anastomosing lines or depressions which may be due in part to compression after the death of the animal.
The endognathite first described bears a considerable resemblance to that figured by Woodward in his Monograph of the British Fossil Crustacea of the Order Merostomata as Eurypterus punctatus. It does not possess the long backward curving spines of Echinognathus clevelandi Walcott, now in the possession of the National Museum.
Remarks. As in Echinognathus clevelandi, the fragments of Megalopterus are not sufficient for a determination of either identity with or differentiation from the Upper Siluric genera, and the generic name is principally the expression of supposed generic distinction based on the Lower Siluric age of the organism. But there stand out a few characters which clearly suggest certain taxonomic relations of the form with the later genera; and these are so similar to those of Echinognathus that they indicate either close relationship or identity in these two Lower Siluric eurypterids. These characters are: the multispinous segments of the endognathite, the peculiar character of the scales and the longitudinal ridges of the segment.
The multispinosity of the segments is a notable character of the genera Stylonurus and Dolichopterus and of a few rather aberrant species of Eurypterus and Eusarcus. The arrangement of the spines in Megalograptus is rather bunched and in this regard differs from the prevailing serial arrangement in Stylonurus and Dolichopterus, and resembles more that of the apparently aberrant Eurypterus dekayi.
The ornamentation consists of circular to oval rings with deep central pits. The ragged edges of the rings show, however, that they are of secondary origin, and since in some places the original scales are preserved, it is seen that the rings originate where the flat or slightly depressed top of the scales is broken away. The scales, where well preserved, strongly suggest the circular disklike scales so characteristic of Eusarcus. They might result from the compression of such wartlike scales as are present in the aberrant Eurypterus pustulosus, and they may also lead to the droplike suboval scales of Echinognathus and of Stylonurus. The comparison with the latter genus is fortified by the presence of strong longitudinal ribs on the segment which is correctly considered by Mr Foerste as belonging to the postabdomen.
- ↑ This shortness may be partly due to a fore and aft foreshortening, as indicated by the pushing of the first tergite under the carapace and by the fold at the frontal margin.
- ↑ E. pulicaris Salter [1863] from the Devonic plant beds of St John, New Brunswick, is based on two minute postabdomina that are insufficient for generic determination and probably do not belong to the eurypterids.
- ↑ Eurypterus scorpioides, in which the chelicerae had been found before by Laurie, is in our view generically distinct and an Eusarcus although on the strength of the presence of equal chelicerae in both, Holm argues for their congeneric character.
- ↑ We describe and figure here the endostoma of Pterygotus, hitherto unobserved [pl. 71, fig. 3].
- ↑ The third was overlooked by the draftsman of the original drawing.
- ↑ The extreme variation in size and location of the compound eyes is due to different direction of compression and has been more fully described under "Remarks."
- ↑ τύλη, knot; πτερόν, wing.
- ↑ See Appendix.
- ↑ The first two are described in the Proceedings of American Philosophical Society, volume 7, 1877, and Second Geological Survey of Pennsylvania, Report of Progress, PPP, 1884, page 31 et seq. E. stylus is described in the last named publication and E. approximatus in the Palaeontology of New York, volume 7, 1888, explanation of plate 27, figure 6. E.potens Hall is not described and the figures [Penn. Rep't, pl. 4, fig. 9, 10] indicate that it is based on unrecognizable fragments.
- ↑ See Appendix.
- ↑ In E. pennsylvanicus and E. approximatus the endognathites are not preserved. The former species is based on a single carapace.
- ↑ Pal. Soc. 1872. v. 26, pl. 25–27.
- ↑ Geol. Mag. n. s. 1887. dec. 3, 4: 481.
- ↑ A drawing of this counterpart was given by Hall loc. cit.
- ↑ In the original description the specimen is erroneously described as presenting a ventral surface.
- ↑ This species was originally described as Eurypterus simonsoni and later referred with doubt to Stylonurus, the author stating that he believes the form to represent a new genus closely related to Stylonurus. The latter reference is based on the surface sculpture and the similarity of a detached part to the long last leg of Stylonurus. The specimen shows the metastoma which, as Schmidt remarks, differs from all other metastomas. In its triangular, pear-shaped outline it agrees completely with that of Eusarcus. The sculpture, also, consisting of disklike prominences with raised margins making horseshoe-shaped impressions, is characteristic of Eusarcus as fully stated in the generic description. The clear photographs of the type of the Russian species show that the general outline and the form of the attached last leg possess the characteristics of Eusarcus. The detached part is not a leg as surmised by Schmidt but the scorpioid slender postabdomen of Eusarcus, and furnishes another character typical of that genus. As to the "Dorsalfurchen" we have the impression that they are accidental. Less pronounced furrows have been noticed by us in various specimens of Eurypterus remipes and other species.
The abdomen appears relatively a little longer than in our species of Eusarcus, possibly through a pulling apart of the segments in anteroposterior direction. - ↑ Other appendages referable to Eusarcus in the Frankfort shale. We reproduce three metastomas which, by their cordiform outline indicate that they probably belong to a type that is either identical or closely related with Eusarcus. The smallest of the three [pl. 84, fig. 10] is covered with flat, round tubercles that agree with those of the integument of E. scorpionis. Another possesses small, granular tubercles [pl. 84, fig. 11].
Our collection also contains the characteristic long conical tail segments and in one case a segment with attached curved telson spine; this and a few tergites suggest the preabdomen of a Eusarcus. - ↑ With the exception of the small Eusarcus obesus (probably a young form) while in the British Eusarcus scorpioides they are as strongly bent forward as in our two species.
- ↑ Original description. Animal measuring over all about 10 to 12 inches or even more in length by 4 to 5 inches in greatest breadth. The length may be allotted on the average thus: Head shield, 2 inches; body, 3 inches; abdomen, 4 inches; tail spine, 2 inches; greatest breadth of body somewhat behind the middle.
Of the appendages the foremost pair is the smallest with about 5 spines on each; the second and largest pair have at least 12, the third about 8, and the fourth about 4 spines. From the second the appendages diminish gradually in size to the fourth.
The large fifth pair reach only to the hind segment of the body—about 3 inches—and show merely the details mentioned in the general description. - ↑ In the smallest specimen they are gently sigmoid in outline, their anterior half being gently concave, a feature that is not observed in the other specimens and quite probably due to differences of preservation, as suggested by a like difference in equal sized specimens of E. scorpionis.
- ↑ A fifth still smaller specimen is in the National Museum. This is so poorly preserved that it is not capable of furnishing positive data. It is, however, of interest in suggesting that the telson was considerably longer than indicated by the other specimens and probably also curved as in the other species of Eusarcus [see pl. 36, fig. 11].
- ↑ As we shall presently show, the metastomes of Stylonurus and Dolichopterus are alike or very similar and the two genera closely related. It is therefore possible that more complete material of the Oesel species will show them to belong to Stylonurus.
- ↑ As before stated, Holm recognized the probable occurrence of this genus in the Baltic provinces by the observation of two metastomes, one of which he has referred to Eurypterus laticeps Schmidt. This species is known only by its carapace which in outline, broad rim, large eyes and ornamentation is very suggestive of the Stylonurus-Dolichopterus group. He also referred an operculum with female genital appendages to Dolichopterus, pointing out its similarity to the corresponding part of D. macrochirus. The opercular appendages of Stylonurus however are not yet known and hence this similarity is not conclusive of identity with Dolichopterus.
Schmidt figured [op. cit. pl. 7, fig. 9] a very interesting leg, referred by him with doubt to Pterygotus osiliensis, and which possesses broad, leaflike spines like those on the last legs of species of Dolichopterus. Holm [p. 56] indicated the similarity of this leg to that of Dolichopterus but suggested that the broad spines are only wrinkles since the limb is very poorly preserved. From our observations of like appendages on the legs of at least two species of Dolichopterus, we consider it probable that Schmidt's figure is correct and that this leg indeed demonstrates the presence of the genus Dolichopterus in the fauna of Rootziküll. - ↑ This elongation is of course shared by the metastoma and obviously induced by the relatively great length of the carapace. But the mouth is further forward in this species than in other genera.
- ↑ Silurus a catfish; in allusion to the form of the carapace.
- ↑ In allusion to the turtlelike head.
- ↑ See also Laurie, 1899, pl. 2, fig. 12, 13
- ↑ Laurie's figure of Eurypterus scoticus [1899, pl. 39, fig. 26] shows on the fourth segment three spines, which would suggest a like feature, but since the succeeding segments clearly possess only two spines it would seem that this appearance of a close series of spines is accidental.
- ↑ Woodward refers this form unhesitatingly to Eurypterus, stating in regard to the fifth pair of legs [p. 483]: "The fifth pair of broad spatulate swimming feet answering to the maxillae, or to the maxillipeds of the higher Crustacea, are not preserved in this fossil; but as they have been found with nearly all the species of Eurypterus hitherto described, there is little doubt that this form also possessed them when entire. Certainly the other appendages reproduce with only slight modification in their style of ornamentation those of the Russian, the American and the Lanarkshire Eurypteri already described and figured by Hall, Schmidt and myself."
- ↑ In specimen figure 2 the apparent posterior margin of the carapace is probably formed by the first segment underlying it.
- ↑ The visual surface itself has not been observed in the individuals of nepionic age, we presume on account of the extremely small size of the specimens and the usual compression of the visual area into a narrow crescentlike band or slit which is very frequently obscure even in the mature specimens. On account of this failure to see the visual surface itself, we must concede the possibility that in this nepionic stage the whole apical or central node may have constituted the visual surface and the latter been gradually reduced to the crescent-shaped band.
- ↑ The carapaces plate 51, figures 10, 13, 14 are obviously affected by lateral compression that shortened the width.
- ↑ Actual measurements are as 13 : 21.5 or 10 : 16.5; 18 : 28 or 10 : 15.5; and 16.5 : 26 or 10 : 15.8.
- ↑ Actual measurements as 15.5 : 23 or 10 : 14.7; 19 : 27.5 or 10 : 14.4; and 20.5 : 28 or 10 : 13.6.
- ↑ In former [fig. 9] to length of carapace as 10 : 37; in latter [fig. 2] as 10 : 27.
- ↑ These are now in the National Museum, and have been kindly loaned by Secretary Walcott.
- ↑ Laurie, 1899, pl. 4, fig. 23, pl. 5, fig. 26.
- ↑ Palaeontology of New York, 3:414*.
- ↑ See N. Y. State Mus. Mem. 11. 1908. p. 247.