The Eurypterida of New York/Volume 1/Pterygotidae
Family pterygotidae nov.
Genus HUGHMILLERIA Sarle
The genus Hughmilleria was erected by Sarle in 1902 for the common species of the Pittsford shale which is thought by its author to show close relation to Pterygotus though in many ways suggesting the genus Eurypterus. The following is the original generic diagnosis:
Type, H. socialis Sarle.
In the elaborate comparison with other genera which Mr Sarle adds to the generic diagnosis, the characters suggesting Pterygotus, as well as the resemblances to Eurypterus and Slimonia, are fully discussed. Since the date of his study the rocks of New York have afforded representations of this interesting genus in the Shawangunk grit and the Frankfort shale. These new forms suggest a somewhat different conception of the relationships of Hughmilleria, which is most conveniently set forth by annotating Sarle's discussion of the relationships of the genus.
As characters suggesting Pterygotus are cited: The rounded triangular or semielliptic outline of the head as seen in Pt. banksii Salter and Pt. raniceps Salter; the marginal, compound eyes; the slender body with slight constriction between the anterior and posterior abdominal portions; the cordate form of the metastoma; and the simplicity of the opercular plate and its appendage. The two forms of this appendage resemble those of Pterygotus as far as the material of the latter permits of comparison, one form being a slender, sagittate-based scale, the other a shorter, broader, convex body, as in Pt. bilobus Salter and Pt. osborni Hall. In the new genus the first form projects posteriorly to protect a shorter lance-linear appendage lying in a cleft of the second sternite, while the second form is followed by an entire sternite without appendage. The sixth pair of cephalothoracic appendages resemble those of Pterygotus in being only slightly expanded distally and consisting of eight joints, with a rudimentary ninth inserted in the end of the palette. The gnathobases have the upright retort form.
The outline of the carapace is very much alike in all species, recalling Pterygotus banksii Salter.[1] The latter, however, is by no means a typical Pterygotus, but in various characters, as notably also the form of the carapace, is quite apart from the other Pterygoti. On the other hand, the carapace of H. socialis resembles most closely that of a species described by Salter and Woodward as an Eurypterus (E. lanceolatus).[2] The latter is, in our opinion, either a true Hughmilleria or a transitional form between Hughmilleria and Eurypterus; at any rate it points to a close relationship of the two genera.
As the second character suggestive of Pterygotus, "the marginal compound eyes" are cited. We see in the structure of these eyes in Hughmilleria strong evidence of the intermediate position of the genus between both Eurypterus and Pterygotus. The facts are the following: It is well known that Pterygotus possesses distinctly faceted compound eyes of elliptic to circular outline, the whole ocular node being occupied by the visual area. In Eurypterus, on the other hand, the facets have never been observed, not even in the transparent specimens studied by Holm, and the visual area occupies only a kidney or crescent shaped space on the outer slope of the eye node.
In Hughmilleria we have found the following condition of the compound eyes. The visual area, in outer view, is always smooth in the hundreds of carapaces we have seen, and without any trace of facets, but an interior view shows unmistakable traces of the facets. These structures are hence present, though very feebly developed.
The compound eye is arcuate on the outer side, but angular on the inner side, as correctly described by Sarle. A laterally compressed specimen [pl. 60, fig. 7] has permitted us to obtain an unforeshortened view of the eye and this shows the kidney-shaped visual area and a triangular palpebral lobe on the inside which is the cause of the angularity.
In H. shawangunk the eyes appear marginal in many specimens, because the marginal portion of the carapace was so impendent that in specimens vertically compressed it becomes folded upon itself and only a portion of the eye is shown [pl. 65, fig. 9]. Wherever the whole carapace is flattened out, the lateral eye is intramarginal by a considerable interspace [pl. 65, figs. 3, 4, 12]. In Pterygotus the lateral eye, at least in the mature stage, is always truly marginal.
Thus we infer that the eyes of Hughmilleria exhibit transitional or intermediate features between Eurypterus and Pterygotus.
The body of Hughmilleria is slenderer than that of the typical Eurypterus, but it falls fully within the limits of the recognized variations of the genus Eurypterus and is much surpassed in slenderness by such forms as E. maria. Similarly the metastoma, while exhibiting a decided tendency to a cordate form, is not nearly so pronounced as in Pterygotus and in general form, stands, about midway between that of Eurypterus and Pterygotus.[3]
The opercular appendages have been considered by Sarle [op. cit. p. 1091] as corresponding in a general way to those of Eurypterus; we see in them strong evidence of the closer relationship of Hughmilleria to Pterygotus; for it is obvious that the appendage in P. anglicus and P. osiliensis is only a more extreme development of that of Hughmilleria by the expansion of the distal end. As a last character suggesting Pterygotus the small distal expansion of the swimming legs is cited. Considering the wide variation in this character within the genus Eurypterus (compare for instance the swimming legs of Eurypterus remipes and E. kokomoensis), this similarity with Pterygotus is of but little import.
As characters distinctive from Pterygotus, Sarle cites the preoral appendages, the spiniform walking legs and the telson. The difference in the preoral appendages is described as follows:
These are stout, three jointed, chelate organs, so short that when extended they barely equal one half the length of the cephalothoracic shield. The pincers are edentulous and bevel-edged and in their normal position lie folded over the basal joints so that their tips converge close to the anterior border of the mouth. Extended, these organs project beyond the border of the shield for perhaps half their length; when turned straight back, their tips lap over the end of the metastoma. In Pterygotus, on the contrary, these organs are very long, having, at least in Pt. bilobus Salter and Pt. macrophthalmus Hall a length fully one third that of the entire animal; and consist of ponderous, dentate pincers supported on a slender, retrally tapering proximal joint of such a length as must necessarily have prevented the pincers being used at the mouth, unless these appendages were somewhat retractile, as suggested by Laurie.
Though the preoral appendages of Hughmilleria are larger than those of Eurypterus they differ still more widely from the very long appendages of Pterygotus with their dentate pincers, but they may well be considered as indicating a tendency to a development of Pterygotuslike chelicerae.
The difference between Pterygotus and Hughmilleria in the character of the spiniform legs, is clearly set forth by Sarle[4] and the slender lanceolate telson is distinctly a Eurypteruslike feature.
To Sarle's comprehensive statement: "Regarding its [Hughmilleria] resemblance to Eurypterus, it might be said that, but for the marginal position of the eyes and relatively large chelae, this form would easily be mistaken for a species of that genus" [op. cit. p. 1090], we may add from the results of our investigations that the facets of the eyes, the character of the opercular appendage and the cordate metastoma are features indicative of a closer relationship to Pterygotus and that we therefore agree with Sarle that it belongs in one group with the latter genus and Slimonia.
Hughmilleria is a good genus that requires distinction as being of a primitive or generalized character, through which it has points of similarity with a number of other genera. It is certain that, notwithstanding its exterior similarity to Eurypterus, it points, by virtue of its cordate metastoma, the intramarginal to marginal position of the compound eyes, the slightly longer preoral appendages, its slender body, less developed swimming legs and the opercular appendage, to the path of development taken by Pterygotus after separation from its common ancestor with Eurypterus. We consequently find the critical characters of Hughmilleria in the same features as did Sarle and Clarke,[5] notably those evinced in the preoral appendages and marginal eyes, as well as in the other features cited, but with the difference that we take them as denoting a primitive condition. This view is strongly supported by the ontogeny of H. shawangunk, for the great similarity of its nepionic and mature growth stages is another proof that Hughmilleria has progressed less beyond the common ancestor of the eurypterids than either Pterygotus or Eurypterus.
Hughmilleria socialis Sarle
Plates 59–63
Hughmilleria socialis Sarle. N. Y. State Palaeontologist Rep't. 1902. p. 1091, pl. 6–9; pl. 10, fig. 1–6, 8, 9; pl. 11–14; pl. 15, fig. 4–6; pl. 24, fig. 1; pl. 25, fig. 1, 3, 4; pl. 26, fig. 3, 5
This is by far the most common eurypterid in the Pittsford shale and is the genotype and best known species. It has been as elaborately described by Sarle as its novelty, its singular features and the excellence of the material deserve. The original description is as follows:
This type is comparatively small, the length of the average individual not exceeding 15 cm. Viewed from either the dorsal or the ventral side, the outline is slenderly lanceolate. In the natural, undistorted condition, the anterior part of the body is flattened, the dorsal and ventral surfaces being slightly convex, while the caudal portion is nearly cylindric.
Cephalothorax. The cephalothorax is semielliptic or subtriangular in outline, the length equaling the breadth at the base, and comprising about one fifth the length of the entire body. Along the gently curving sides and acutely rounded front is a narrow flattened border, striated on the under surface, and not exceeding a fraction of a millimeter in breadth. The dorsal surface is slightly rounded or arched from the side to the center, so that in an undistorted shield 22 mm long, the elevation is about 2 mm. The posterior edge, except for a slight forward curve at the genal angles, is straight. The compound eyes barely break the outline of the shield; they are small, elongate, widest anterior to the middle, the outer side arcuate, the inner formed by three nearly straight edges—a short basal and a little longer anterior, forming slightly rounded obtuse angles with a long inner side. The anterior end of the eye is acute. The length of these organs on the cephalothorax, the dimensions of which were given above, is 5 mm. However, the usual proportion between the length of the shield and eye is as 1 : 4.5. A line drawn connecting the posterior ends of the eyes passes through the center of the shield. The ocelli are situated on a small tumescence cut by this line; they form two minute, ringlike prominences separated by about the length of their diameter.
Abdomen. The abdomen, at the widest point, or between the third and fourth dorsal segments, is a little wider than the base of the cephalothorax. Thus, in one animal measured, these dimensions were respectively 24 mm and 17.5 mm, in a second 23 mm and 17 mm, and in a third 33 mm and 26 mm, probably varying somewhat according to the amount of compression and also somewhat with the animal. From this point the abdomen tapers very gradually to the telson; it is divided into anterior and posterior parts, easily distinguished by their structure. The preabdomen consists of six dorsal and five ventral, transverse plates; the postabdomen of six annulate segments and one spiniform.
Preabdomen. The first tergal plate of the preabdomen is very narrow and is overlapped by the posterior margin of the shield. Its posterior edge is slightly convex, and its ends are rounded. The second segment is twice as long as the first, its posterior edge is slightly concave along the middle portion, and the posterior angles are rounded, while the anterior are produced, to make up, as it were, for the rounding away of the preceding tergite. The succeeding tergites are very nearly equal in length, the fifth being perhaps a little the longest, and are about one third longer than the second. The posterior margins are concave as in the preceding, but straighter near the sides, forming almost right angles.
The first ventral plate, or sternite (the operculum), is one third as long as broad, and is divided along the axial line into two equal parts. These are rounded off at the lateral angles, particularly the anterior, and excavated along the median line for the reception of the opercular appendage; the posterior edges are slightly projected on either side of this, while the anterior inner angles are projected forward, forming a compound median lobe. The second sternite, in the female, is nearly as long as the operculum, and is deeply cleft for the reception of an appendage nearly equal to it in length. The sides are cut obliquely forward, making the posterior angles rather acute; the anterior angle forms small lobes, and the middle of the anterior edge is slightly produced. In the male the last four sternites, and in the female the last three, do not differ materially from the last four and three abdominal tergites. The relative position of the several plates of the sternal series to those of the tergal, is as follows: the opercular plate begins a little farther forward than the first tergite, but, owing to its greater breadth, lies beneath the line of overlap of the first and second tergites, while the second sternite lies beneath the overlap of the second and third tergites, and so on, the last sternite underlying the overlap of the fifth and sixth tergites, thus not extending as far back as the posterior edge of the sixth tergite.
Postabdomen. The first postabdominal segment consists of a tergal and a sternal portion united by their appressed pleural ends. The postlateral angles are prolonged into short, bladelike lobes which extend alongside the following segment for fully half its length. The tergal portion is the longer, and its posterior edge forms a broad lobe; the sternal portion is short, and its posterior edge is straight, while its anterior edge extends forward to meet the last sternite of the preabdomen. The following five segments are plain, bandlike rings, decreasing in breadth backward. In the first the breadth is considerably greater than the length; in the last, or penultimate body segment the length and breadth, in compressed specimens, are equal. The anterior end of each of these segments is marked by a groove for the attachment of the interarticular membrane.
The telson is very slenderly lanceolate, widest near the anterior end and attenuated at the tip. In length it is equal to the four preceding segments. The dorsal surface is convex, rising from sharp, lateral edges to a median longitudinal carina, which begins in the anterior part as a broad, angular prominence; the ventral surface is nearly flat or faintly convex; a cross section is thus subtriangular. Compression usually flattens the sides and thus heightens the angular appearance. The uncompressed specimen has a length of 31 mm and a greatest breadth of 7 mm.
On the ventral surface of the cephalothorax, in front, is a convex lobe or platform, the epistoma, from which extends a flat, tapering doublure ending in a small expansion at the genal angles. In molting and also from compression, the epistoma divided through the middle rather than along the sides.
Appendages. The preoral appendages are short, stout, three-jointed, chelate organs attached at the posterior border of the epistoma. The two distal joints of each form a pair of broad based, edentulous, bevel-edge pincers, in the ordinary state of compression having a breadth equal to one half the length. The blades are about equal in length to the basal portion and meet at the very acute, slightly curved tips and again, usually, only near the base. There is considerable variation in the relative form of the pincers, as shown on plate 11. The broad basal joints are about one fourth longer than the pincers, widest near the base and longest on the inner side, and in the natural position extend beyond the anterior margin of the shield for about one third their length. The pincers articulate with this joint in such a way that, when folded backward, they cross it obliquely, and their tips converge a little in front of the mouth; when extended forward, they diverge somewhat. The preoral appendages could also be turned back to their full length over the mouth, the pincer tips then overlapping the metastoma. In an individual having a cephalothorax 22 mm long, the preoral appendages are 10 mm long.
The four pairs of endognathites, or crawling legs, do not differ materially from one another except in length. The anterior limbs are somewhat shorter than the extended preoral appendages, and their tips extend but very little beyond the margin of the shield. Each succeeding pair is about one half longer than the preceding, so that the last limbs are probably four times as long as the first. All have seven joints, of which the terminal is spiniform. The third to the sixth joints inclusive carry ventrally and at the distal ends a pair of striated, slightly curved, slender spines. The inner spine of each pair is the longer, and the length increases for each successive set, from the third to the fifth joints; the spines on the sixth are short. The coxal joints are elongate, slightly curved, widest at the base and equal in length to the succeeding two joints. They increase in length with each successive pair, and bear on the inner end a series of 15 or more, sharp, curved teeth, which decrease in size from the front. On each of the fourth coxal joints is a large perforation of the upper side near the fixed end. No epicoxite has yet been observed. The second joint of the endognathite is divided by constrictions into three transverse sections. It is articulated at the fixed end of the coxal joint and is fully two thirds as wide.
The limbs of the sixth pair are narrow and paddlelike, and consist of eight joints and a rudimentary ninth or claw, the seventh and eighth forming a slightly expanded blade. The seventh carries a large, subtriangular, lobelike plate, nearly one half as long as the joint proper, marked off from the inner, distal end by a suture. The eighth, or palette, is elongate oval with the margin finely incised, and carries the minute claw inserted in a notch on the inner side near the tip. On the dorsal surface of the seventh and eighth joints, at the proximal end and outer edge of each, is a group of minute, craterlike tumescences, which were probably receptacles for the bases of hairlike bristles. In a swimming arm 29.5 mm long, exclusive of the gnathobase, the narrowest joint or the fourth, measures 5 mm across; from this point the arm gradually enlarges to 6.8 mm on the seventh and eighth joints. When the swimming arms are turned back, they reach the line of the fourth or fifth dorsal segment. The gnathobases have the form of an upright retort. The inner extremity of each is provided with from 18 to 20 sharp, slightly curved teeth, which become finer posteriorly. A gnathobase, accompanying a cephalothoracic shield 22 mm long, is 16 mm long; the width of the narrow necklike portion 6 mm; the width at the base 13 mm.
The metastoma is elongate cordate, the greatest breadth coming anterior to the middle. The smaller, or posterior end, is truncated and has rounded corners. The anterior notch is rather deep and broad. A comparison of the length to the greatest breadth of several metastomas gives the proportion of 2 : 1. In an individual having a cephalothorax 23 mm long the metastoma is 16 mm long.
The genital appendage differs noticeably in the two sexes. In the female it consists of two parts, one carried by the operculum, the other by the second sternite. The opercular appendage is a slender, sagittate-based, convex, scalelike sheath projecting for about one fifth its length beyond the posterior edge of the operculum and appearing to be formed by the fusion of two parts. The anterior of these includes the sagittate base and a narrower, more convex portion with a flattened border on either side. Its distal end is reentrant and fused to the posterior part. This part is a little narrower, slightly tapering and beveled in from either side for one fourth the breadth, to the sides of a slightly raised platform which is flat-topped for the greater part of its length, but becomes concave posteriorly, forming a shallow groove at the abrupt end. The terminal angles are noticeably truncated. The appendage carried by the second sternite is partially covered by that of the operculum. It is very slender, its greatest breadth not exceeding one sixth the length. The anterior half is sublanceolate with a triangular base; the posterior is attenuate and terminates just within the end of the cleft. In the male the appendage is simpler and confined to the operculum, the following sternite being entire. It is wider and somewhat shorter than that of the female, the average length being only about two and one half times the breadth. It is convex, broadly lanceolate and slightly produced at the posterior free end which just clears the edge of the operculum. A specimen in which a portion of this organ is scaled away gives a cast of the interior showing small elevated lines radiating from near the center backward, and may possibly represent part of the vascular, or duct system of this organ. The two sexes are about equally represented in numbers.
The whole surface of the body is covered with imbricating, crescentlike or angular scales, sometimes carrying smaller ones of the same pattern. These scales are so minute on certain areas as to appear almost obsolete. They are most conspicuous on the ventral side of the preabdomen and appendages. On the cephalothorax and abdomen the scales point backward, on the paired appendages toward the distal end, and on the epistoma, forward.
This singular creature has the appearance of an Eurypterus with the carapace of a Pterygotus. The Pterygotuslike aspect of the carapace is principally due to the marginal position of the compound eyes.
Another character worthy of mention is the ornamentation,[6] which consists of flat, imbricating scales that are crescentlike near the anterior margin and become angular posteriorly. They are evenly distributed over the entire body, carapace [pl. 60, figs. 6, 8], endognathites, metastoma, operculum and its appendages, save the telson where they have not been observed. On the distal segments of the endognathites they appear as small tubercles.
The telson agrees in its slender, spinelike outline with that of Eurypterus. But while that of Eurypterus is flat on the dorsal side and bears a carina on the ventral side, that of H. socialis is flat on the ventral side and carinate on the dorsal.
Horizon and locality. Pittsford shale at Pittsford, N. Y.
Hughmilleria socialis var. robusta Sarle
Plate 63, figure 16
Hughmilleria socialis var. robusta Sarle. N. Y. State Palaeontologist Rep't. 1902. p. 1097, pl. 21, fig. 1, 2
A few fragments have suggested the presence of a larger variety of socialis in the Pittsford shale on which the following notes were made by Mr Sarle:
What appears to have been a varietal form of Hughmilleria socialis is represented by a nearly entire abdomen, two first ring segments and an imperfect metastoma.
The features which distinguish this form are: its larger size; proportionately much greater breadth; the greater convexity of the dorsal posterior edge of the first ring segment and, in some cases, the division of this edge into two, broad smooth lobes; the more noticeable contraction of the abdomen at the second ring segment; and the more rotund form of the metastoma.
The abdomen found lies in the shale dorsal side up, showing the anterior nine segments well preserved. The second and third ring segments are partially disconnected. The breadth of the preabdomen at the widest point, or between the third and fourth segments, is 51 mm, its length 56 mm, the breadth of the first ring segment is 42 mm, of the second 30 mm. The dorsal posterior edge of the first ring segment is entire and very noticeably convex. In each of the isolated ring segments a broad, deep notch produces a bilobation of this edge. A line of pittings close to this edge shows this feature to be natural. The proportions of the most perfect of these segments are: breadth 43 mm length of the dorsal side 22 mm, length of the ventral 11 mm, length of the postlateral lobes 8 mm. The metastoma associated with one of these segments is apparently of a smaller individual and lacks the anterior notched end. At the widest part it measures 14 mm, and from there to the posterior end, 14 mm.
It was at first thought that the distinctive features of these specimens might be merely old age characters of H. socialis, but larger individuals of that species seem to show the same relative proportions as the smaller. However, it is considered that the differences shown by the incomplete material of the collection are not, of themselves, sufficient to warrant the founding of a distinct species.
We have not obtained any further material that would qualify the inferences here set forth.
Horizon and locality. Pittsford shale at Pittsford, N. Y.
Hughmilleria magna nov.
Plate 85, figs. 11–19
Description. Carapace semielliptic, length and basal width subequal, lateral margins gently curved, subparallel, frontal margin bluntly angular so as to form a triangular front to the carapace. Posterior margin straight transverse or very slightly concave; genal angles roundish rectangular.
Lateral eyes large (a little more than one third the length of the carapace), submarginal, oval in outline. Ocelli subcentral, their tumescence between the posterior ends of the lateral eyes.
No ornamentation has been observed on the carapace.
Horizon and localities. Frankfort shales. The great majority of the specimens are from the Dettbarn quarry at Schenectady, where in one layer the species is quite common. A few carapaces have also been found at Duanesburg and Rotterdam Junction, Schoharie county.
Remarks. The form of the carapace is subject to much variation in outline, obviously through the stretching and wrinkling of the thin, drifted integuments in various directions. The carapace selected as the type [pl. 85, fig. 11] is smooth and but little distorted. When the test is completely flattened out, the lateral eyes are seen to be separated from the margin of the carapace by a narrow strip, half as wide as the eye, contracted forward and broadening backward as in the genotype.
The type measures 17.5 mm in length and 20 mm in width. The eyes are 7 mm long. Several carapaces indicate that this species reached much larger dimensions than its supposed later allies. The original of plate 85, figure 16 is 58 mm wide and 42 mm long. Its lateral margins are completely flattened out and the specimen somewhat compressed in the axial direction.
Besides the carapaces, on which the species is based, a half complete specimen [pl. 85, fig. 13] has been obtained. This exhibits a form of the preabdomen corresponding to that of H. socialis, the genotype, if the slight axial contraction of the specimen is taken into account. The swimming leg of the right side can be distinguished in its outline. It is relatively longer than that of H. socialis.
Besides the carapaces two detached chelicerae resemble in their strong development and long pointed pincers more those of Hughmilleria than of any other genus [pl. 85, fig. 17, 18] and also detached body rings [pl. 85, fig. 19] exhibit a type of ornamentation, consisting of transverse lines near the anterior margin, known to us only in H. shawangunk, the Otisville representative of the genus.
Hughmilleria shawangunk Clarke
Plates 64–66; 69, figure 1
Hughmilleria shawangunk Clarke. N. Y. State Mus. Bul. 107. 1907. p. 308, pl. 4, fig. 1–4; pl. 5, fig. 1–9
Description. Hughmilleria shawangunk attains but half the size of the genotype, or about 8 cm and is therefore one of the diminutive species of eurypterids. In outline of body and form of head it closely resembles H. socialis; it is slender and terete, but slightly wider in the middle of the preabdomen than at the base of the carapace, and lacks any marked contraction from preabdomen to postabdomen. With the anteriorly rounded, subtriangular carapace and marginal eyes, the dorsal aspect of the animal is singularly fishlike and suggestive of great agility.
Cephalothorax. The carapace is semielliptic in the mature form, wider than long by one sixth to one fifth, comprises one fifth the length of the body or more; as preserved it is subject to great variations in outline, mostly due to variously directed compression and wrinkling after entombment and to an originally thin test. The lateral margins of the carapace are slightly convex, the frontal part acutely rounded. The posterior edge is very gently concave forward, nearly straight. The dorsal surface was uniformly and strongly convex, culminating between the lateral eyes and somewhat impending along the sides. A narrow flat border surrounds the lateral and frontal margins. The compound eyes are of medium size (one fourth to one fifth of length of carapace), intramarginal in position, separated from the margin by an interval nearly as wide as the eyes themselves. On account of the position of the eyes on the impending sides of the carapace, however, they appear in most compressed specimens to be marginal [pl. 64, fig. 13; pl. 65, figs. 1, 6, 9]. They are placed so far forward that they are distant only their own length from the foremost point of the carapace. The form of the ocular node resembles that of an elliptic sector, the outer margin being rounded and the inner margin angular or composed of two, frequently unequal radii, the anterior being the longer. The anterior end of the node is acute, the posterior rounded. The node is so slightly prominent that the eyes hardly project beyond the outline of the carapace. The visual surface is crescentlike with somewhat swollen extremities [pl. 65, fig. 10] and situated along the outer edge of the ocular node. The ocelli are distinct, separated by the length of their own diameter, and situated on a flat circular tumescence that lies on a line connecting the inner angles of the compound eyes.
Abdomen. The abdomen is slender, increases slightly in width to the fourth dorsal segment and then tapers very gradually to the telson. Its greatest width is about one fourth the length of the body.
Preabdomen. The tergites [pl. 66, figs. 6, 8, 11] are narrow, subrectangular bands with anterior and posterior margins straight or but slightly bent forward, three to four times as wide as long, save the first which is six and one half times wider than long, or in other words, is a very narrow band. The anterior edge of the latter is straight, the posterior gently concave. The antelateral angles are broadly rounded and produced forward and the postlateral angles slightly extended posteriorly so that both extremities of this segment are widened. In the following tergites the antelateral lobes are very small [pl. 66, fig. 6] or altogether absent in the last.
The opercular plate has not been observed. The sternites [pl. 66, figs. 7, 10] are longer than the tergites, their anterior and posterior margins similarly subparallel and curve gently forward. The antelateral angles are furnished with blunt triangular lobes while the postlateral angles are well rounded.
Postabdomen. The postabdominal segments [pl. 66, figs. 5, 9] are annular, gradually increase in length and decrease in width posteriorly, so that while the first is three times as wide as long, the last is about as long as it is wide at its proximal articulation. The postabdomen is about one third of the body in length and decreases by one half its width from the first to the sixth segment. The first [fig. 5] postabdominal segment is produced into long bladelike lobes which attain nearly half the length of the segment; the others [pl. 66, fig. 9] possess only small acute postlateral lobes. The posterior doublure is distinct and occupies about one fourth the length of the segment.
The telson is identical with that of H. socialis; it is lanceolate, relatively short (not one fifth the length of the body) and apparently convex on the upper and flat on the under side. It is slightly contracted at the proximal end and widest at about one third of its length. The dorsal surface carries a median carina which begins a little behind the anterior edge of the telson and continues to the point. The lateral edges are sharp and furnished with a thickened, flat border.
Appendages. Our knowledge of the appendages of this species is still very incomplete as but very few entire specimens have been obtained and they show only traces of these organs. The crawling legs appear to have been both short and slender as in H. socialis. The swimming legs have been seen in two specimens [pl. 65, figs. 6, 8]. They are small (extending when reflexed to the fourth tergite) and slender. The fourth, fifth and sixth articulations are nearly equal in length, and gradually widen. Their distal edges are lobed or fringed. The seventh and eighth segments form a slightly expanded oar plate, the seventh being slightly longer than the eighth and bearing a large distal lobe on the inner side. The eighth segment is oval in form, its distal end distinctly acute with a small terminal subcircular ninth segment [pl. 65, fig. 8].
The coxa of the last pair of legs is probably represented by figure 1, plate 66, for these bodies show the outline of the corresponding organ in the genotype and possess a system of fine anastomosing lines characteristic of the sculpturing of H. shawangunk. Sarle compares the shape of this coxa in H. socialis to that of an upright retort and records the presence of 18–20 sharp, slightly curved teeth on the manducatory edge. The coxa here figured exhibits a stronger neck and longer manducatory edge, but exactly the same number of teeth. Another coxa, reproduced in the preliminary paper [op. cit. pl. 8, fig. 10] also possesses a system of fine lines as shown in our figure [pl. 66, fig. 2] but is of more compact form and with shorter neck and smaller number of teeth, the first of which is longer than the rest. This is possibly the coxal joint of an endognathite.
The metastoma has not been seen well preserved in position, but we refer several metastomas to this species [pl. 66, figs. 3, 4] because they possess, on one hand, the form of that in H. socialis and on the other exhibit a peculiar striated ornamentation apparently characteristic of H. shawangunk. These metastomas are elongate cordate, broadest anteriorly to the middle, with cordate or deeply notched anterior and an evenly rounded posterior extremity in some and a truncated one in other specimens.
The genital appendages have not been seen.
The ornamentation is most characteristic. It consists on all segments of a series of fine striae, running parallel to the anterior margin, most crowded near this margin, farther apart and fainter posteriorly, disappearing at about the middle of the segment, save on the postabdominal segments where they can be traced to near the posterior edge. Near the lateral edges of the tergites they bend sharply backward, finally coalescing with the border and gradually disappearing. On the sternites another characteristic set of striae is added posteriorly of the frontal set. The second set consists of curving striae running obliquely backward and inward from the antelateral angles and lateral margins [pl. 66, fig. 10] and connected by anastomosis with the frontal parallel line. Along the lateral margins they are dissolved into a meshwork of lines. Like systems of lines appear on the metastoma, where they pass transversely across, with a slight forward convexity, and on the coxa where they strongly anastomose. The coxal segments and the metastoma were also furnished with a fine striation.
Ontogeny. The ontogeny of H. shawangunk is well shown in the small series of individuals reproduced on plate 64. The most interesting of these specimens is the original of figure 1 which is but 2 mm long and very distinct. This larval form is a clear representative of the nepionic growth stage. It still lacks two, possibly three, segments of the full complement of twelve. Its most important feature is the remarkable general similarity to the mature stage of the species, in the slenderness and form of body, form of carapace and eyes and position of the latter. Its most distinctive larval characters are (1) the relatively greater size of the carapace, (2) the relatively great size of the compound eyes, (3) the smaller number of segments.
The carapace in the nepionic stage attains one fourth the length of the body, while in the ephebic stage it reaches only one fifth. The head is also broader than the rest of the body while in the mature specimens the greatest width is reached in the middle part of the preabdomen. It also seems that in this and the following growth stages the head is relatively somewhat shorter in outline than in mature forms (by about one eighth of the width) and slightly more rounded in front.
The compound eyes do not differ in location from those of the mature individuals, being intramarginal and separated by a small interval from the margin, but they are markedly larger, occupying one half the length of the carapace as compared with one fourth to one fifth in the mature stage. They are likewise distinctly more prominent; at least in the specimens representing the neanic stage.
There are nine distinct segmental division lines in the nepionic specimen, indicating the presence of nine segments, with possibly a shorter tenth one directly behind the head. There is a slight break in the outline at the end of the third segment, the fourth setting in a little further. This feature suggests that the postabdomen was already complete and consisted of six segments, while the preabdomen possessed thus far only three to four segments. This inference is supported to some extent by the fact that the postabdominal segments already exhibit the proportions of the mature forms in their gradual narrowing and lengthening. It is therefore probable that the new segments, at least the tergites, are added in successive moltings in the preabdomen, perhaps directly behind the carapace, as in the trilobites; or in other words, that the head and tail appear first and the thorax is completed gradually.
The swimming legs are also shown in the nepionic specimen. They are relatively shorter and broader than in the mature age.
The telson spine is of the same form and proportion to the body as in the ephebic stage.
The neanic stage is represented by the originals of the figures 1–11, 13. The first two of these are fair representatives of the earliest neanic (ananeanic) stage. They still retain the nepionic proportions of the carapace while the eyes have already been reduced to about one third of the length of the carapace, but are still distinguished from the ephebic eyes by their greater prominence. The large size of the ocellar mound and the distinctiveness of the ocelli themselves are also a characteristic feature of this stage [figures 1–3]. The carapace is surrounded by a thick, flat border in these specimens, possibly the doublure of the underside, exposed by the breaking away of the upper margin. The preabdomen is complete in one of the two specimens and remarkable for its uniform width which is equal to that of the base of the head. As specimen figure 13 shows, this width still remains nearly uniform in individuals a little older, while a somewhat abrupt reduction takes place to the postabdomen at the first postabdominal segment. This is the first stage in which the fine transverse sculpture lines could be recognized [pl. 64, fig. 5].
Horizon and locality. This species is one of the most common forms in the fauna of the Shawangunk grit at Otisville, N. Y.
Remarks. H. shawangunk differs from the genotype in its smaller size, somewhat broader carapace and most distinctly in the surface sculpture which is characterized by parallel, transverse striae, absent in the other species.
Genus PTERYGOTUS Agassiz
Pterygotus will always be historically associated with the rocks of Scotland which carried the "seraphim" of the quarrymen, the type 
Figure 70 Restorations of Stylonurus powriei (1) and Pterygotus anglicus (2) in Page's Introductory Text-book of Geology. ed. 5. 1859. p. 71 of Agassiz's P. anglicus, and later afforded the material for the monographs by Huxley and Salter [1859] and by Woodward [1866]. The British rocks have altogether yielded nine species of Pterygotus, two of which, P. anglicus and P. bilobus, are known in complete specimens. The fragments of several of these species have left no doubt that the individuals attained gigantic proportions and surpassed all other then known Merostomata in size. Schmidt's work [1883] on the merostomes of the Eurypterus beds of Oesel contains a very elaborate description of the Pterygotus, P. osiliensis, and corrects several misconceptions of the preceding authors in regard to the structure of the genus. Above all it established the number of walking legs to be four pairs, Woodward having assumed but three, and it recognized the proper position of the epistoma. Ten years after Schmidt's publication Laurie discovered the epicoxite and the second (female) form of the opercular appendage. The New York rocks furnished to Hall only fragments of the genus on which he based three species, P. cobbi, P. macrophthalmus and P. osborni. The waterlime quarries at Buffalo have since afforded somewhat more extensive series of these remains, some of the specimens excellently preserved. Grote and Pitt [1877] and Pohlman [1881–86] made use of some of these, basing thereon descriptions of six alleged species, all of which have proved to belong to two forms, Hall's P. cobbi and a new type, here recognized as P. buffaloensis (Pohlman). A fossil from the same locality described by Pohlman as a Ceratiocaris, is the telson of a gigantic Pterygotus (P. grandis). Finally the Pittsford shale, the dark shale of the Shawangunk grit, and the Frankfort shale, have furnished representatives of other species, viz, P. monroensis, P. globiceps, P. prolificus and P. nasutus, all of them as yet very incomplete. As Hall's species P. osborni has proved to be a synonym of his P. macrophthalmus, there remain out of the considerable number of proposed species of Pterygotus from the New York rocks, only eight whose differentials can now be regarded as satisfactorily determined, viz:
| P. macrophthalmus Hall | P. grandis (Pohlman) |
| P. cobbi Hall | P. monroensis Sarle |
| P. buffaloensis (Pohlman) Clarke & Ruedemann | P. prolificus nov. |
| P. globiceps nov. | P. nasutus nov. |
On this continent no Pterygoti have been found outside of New York and only two of the New York species (P. macrophthalmus and P. buffaloensis) are known in entire specimens, all the others being based on carapaces, chelae or telsons. The material of these two species, however, is so complete that it has allowed a detailed description of the forms and some additions to our knowledge of the structure of the genus. Among these is the demonstration of the identity of the structure of the "chelate antennae" of Pterygotus with the chelicerae of Eurypterus and their composition of but three segments (as already suggested by Laurie) instead of eight as formerly assumed; the demonstration of the identical structure of the compound eye of Pterygotus with that of Limulus and the determination of the endostoma.
The characteristics of this genus consist in the lack of distinct differentiation of the body into preabdomen and postabdomen; the large size of the compound eyes, their marginal position and distinct facets; the presence of a distinct epistoma, the enormous development of the preoral, chelate appendages, the slenderness and lack of spines on the four pairs of walking legs, the heart-shaped, deeply emarginate metastoma and the broad telson.
Huxley and Salter placed P. bilobus in a separate subgenus, Erettopterus, on account of its bilobed telson. While some have recognized this group as a distinct genus, others have not given it even subgeneric rank. Laurie states that the species with such telsons "might fairly be separated from the rest as a subgenus, were it not that the frequent absence of the tail would make such an arrangement highly inconvenient." In our view the recognition of a natural group can not be a matter of convenience, but is of necessity, when the differences are recognized as subgeneric in rank. Erettopterus is represented in our Siluric rocks by P. grandis of the Bertie waterlime, P. globiceps of the Shawangunk grit and certain telsons from the Frankfort shale.
The presence of Pterygotus in the North American Devonic has been shown by Logan, Billings and Clarke, in the Grande Greve limestone (Lower Devonic), by Dawson in the Gaspé sandstone, by Clarke in the Dalhousie formation and by Whiteaves in the Upper (?) Devonic at Campbellton. All these remains from Eastern Canada are fragmentary and only those of Campbellton have justified description (P. atlanticus).
Pterygotus macrophthalmus Hall
Plate 69, figures 2–7; plate 70, figures 1, 2; plate 71
Pterygotus macrophthalmus Hall. Palaeontology of New York. 1859. 3: 418*, pl. 80A, fig. 8, 8a
Undet. crustacean. Ibid. pl. 80A, fig. 6
P. osborni Hall. Ibid. p. 419*, pl. 80A, fig. 9
Description. Cephalothorax. Outline of carapace or cephalothoracic shield semielliptic. In the type of the species, the carapace of a young individual, the lateral margins converge but slightly forward; the anterior angles formed by the projecting eyes and the anterior margin being well rounded. In mature carapaces the lateral and anterior margins are less rounded and more nearly straight, the lateral margins subparallel. The posterior edge is slightly incurved. The surface is very gently convex, and seems to have been originally rather uniformly, but very moderately, elevated with a slight depression along the medio-anterior margin of the compound eyes. The latter are subelliptic, very prominent, project beyond the margin of the carapace and are located at the antelateral angle of the cephalothorax. Their length is nearly one half that of the lateral margin of the cephalothorax; their distance from each other is distinctly less than the length of the eye. As more fully stated in the generic description, the compound eyes are entirely smooth in their exterior view, the facets becoming visible only when the exterior layer of the cornea has become split off or on an interior view. The facets are small and squarish in shape. The ocelli are borne on a small oblong or rhomboidal tumescence, situated in a line connecting the bases of the marginal eyes, and sometimes prolonged posteriorly in a crest. The ornamentation consists of an extremely fine granulation evenly distributed over the carapace, becoming coarse between the compound eyes.
A relatively narrow doublure surrounds with uniform width the frontal and lateral margins of the cephalothorax. The doublure at the base of this shield is three times as wide; it follows the entire posterior margin, thus making the doublure ring complete.
Abdomen. The abdomen widens to the third or fourth dorsal segments, where, in mature individuals, it seems to have been wider by one fourth than the base of the cephalothorax. From this point it tapers very gradually to the telson.
Preabdomen. The first of the six tergites is shorter by one half than the following ones. It is a narrow band, rather strongly curved fonvard in the middle portion and rounded at the ends. The following tergites are relatively broad, their length amounting to one third of their width. The middle portion forms a broad lobe while the pleurae or epimera are projected forward somewhat more abruptly. The fifth tergite is the widest, while the fourth and sixth tergites are about equally long; the fifth surpassing the other two but very little.
Along the posterior margin extends a broad doublure, amounting to one third the length of the tergite, bending forward at the postlateral angles, thence rapidly narrowing and ending a little behind the antelateral angle. Each anterior tergite overlapped the following one to an amount equal to the width of the doublure.
Such well developed "ears" at the antelateral angles as are figured by Woodward (P. anglicus) and Schmidt (P. osiliensis) have not been observed by us, but our evidence on this point is rather scanty and the following sternites of this species have been seen only in fragmentary condition.
Postabdomen. The five first postabdominal segments are, on the whole, simple broad rings, indicating that the original form of the postabdomen approached a conical shape with circular sections. There existed, however, a slight flattening along the lateral lines, in continuation of the pleurae or epimera of the tergites. The edge of these alae, at least in the fourth and fifth segments, is thickened and provided with a somewhat coarser sculpture. The anterior and posterior margins are practically straight with a slight protrusion of the antelateral corners. The doublure of the posterior margin is narrow.
The sixth postabdominal segment differs materially from those preceding both in shape and size. It is longer by one third to one half than the penultimate segment, possesses more convex lateral margins, which are serrate on their posterior half, and indications of a dorsal median crest extending over the posterior half.
The telson is obovate, one sixth longer than wide in mature specimens, and one fourth longer in young ones. It surpasses the ultimate segment in length by nearly one half but equals it in width. It is strengthened by a thick ridge along the middle line which runs out into a blunt posterior spine. The lateral margins are smooth anteriorly, but bear on the posterior part irregular serrations, which increase in size posteriorly and along the posterior edge consist characteristically of an alternation of one large serra with three or more minute denticulations. The ventral side of the telson was apparently provided with a less prominent keel, though the evidence on this point is not very conclusive.
Appendages. The epistoma, with one of the marginal shields adhering, has been found in one example [pl. 71, fig. 3]. It is a four-sided plate, bounded by a convex anterior, a deeply emarginate posterior, and two broadly concave lateral margins. It is separated by a suture from the triangular marginal shield. Its sculpturing, consisting of crescentic scales with the convexity turned forward, is distinctly seen and verifies by its direction Schmidt's inference that the epistoma, like the marginal shields, originates from extensions of the marginal doublure of the carapace.
The preoral appendages or chelicerae have been found in only one case in connection with the body [pl. 70, fig. 1]. They are in all particulars identical with the more fully known chelicerae of the closely related P. buffaloensis, with the exception of the less prominence of the distal point of the free ramus, thereby indicating a slight approach to P. cobbi. Professor Hall figured a fragment of a free ramus of a chelicera on his plate 80A, figure 6, without determining its relations.
The four pairs of walking legs or endognathites are so thin and slender that they are rarely preserved. They are well seen in Hall's type of P. osborni [pl. 71, fig. 6]. Another still better preserved leg is reproduced in plate 71, figure 8. This resembles an antenna in its whiplike form and exhibits seven segments, the first two of which are short, the other long and tubular, the middle one being the longest, while of the last only a short fragment is seen. The type of P. osborni shows also traces of clublike widened coxal segments. The exact number of these we have been unable to establish. They were relatively longer and more slender than those figured in the restoration of the British forms and of P. osiliensis.
The swimming legs are small as in all Pterygoti; when turned back they do not reach the anterior margin of the fourth tergite.
The gnathobase is like that of P. buffaloensis; and it probably possessed a like relation in size to the swimming leg and carapace.
In regard to the other joints of the swimming leg, we may also refer to the full description of these parts in the larger species from Buffalo, there being no specific differences apparent in these organs.
The metastoma is elongate cordate; its greatest width, which is a little beyond the middle, is about one half the length. The anterior margin is deeply emarginate, the posterior part contracted and the posterior end somewhat acutely rounded.
The endostoma has not been observed [see P. buffaloensis].
The opercular appendages have not been preserved favorably in any of our specimens. The type of P. osborni [pl. 71, fig. 6] retains only the posterior portion of the operculum, together with the corresponding part of the opercular appendage, which indicates a short subtriangular organ that would correspond to the appendage of the male of other eurypterids. Near the broken edge the margin of an emarginate lobe is exposed and the posterior angle bears two dark spots suggestive of pores. The opercular appendage of the female has not been observed by us in this species.
The ornamentation agrees with that here described of P. buffaloensis.
Measurements. The few fairly complete specimens at our disposal are immature individuals. The specimen on plate 69, figure 2 gives the following measurements:
Length of carapace about 25 mm
Width, about 35 mm
Length of largest tergite, 11.5 mm
Width, 44.5 mm
Length of first postabdominal segment, 11 mm
Width, 39 mm
Length of last postabdominal segment, 16.5 mm
Width, 21.5 mm
Length of telson, 33 mm
Width, 23 mm
Total length of original specimen (not distended as in fossil state), 184 mm
Largest carapace observed:
Length of carapace, 28.5 mm
Width of carapace, 40.5 mm
Length of tergite, 23 mm
Width, 73 mm
A very large tergite [text figure 71] collected at Litchfield and possibly belonging to this species, has a length of 10 cm and a width of about 37 cm.
The largest telson observed measures:
Length, 60.5 mm
Width, 49 mm
This telson, which undoubtedly belongs to P. macrophthalmus, indicates that the species attained at least twice the size of the complete individual represented on plate 69, figure 2 or a length of a foot and a half. If the large tergite from Litchfield belonged to this species, the animal reached a size of about 1.65 m or 5 feet, 5 inches.
Remarks. The species P. macrophthalmus was founded upon the carapace of a young individual from the waterlime at Litchfield, Herkimer co., N. Y. At the same time a specimen lacking the carapace, and showing only four segments of the abdomen and the ventral side of the cephalothorax was made the type of another species, P. osborni. This specimen came from the same horizon, and a locality a few miles distant from Litchfield, viz, Waterville, Oneida co. A separate metastoma [op. cit. pl. 80A, p. 16] of the same shape as that shown in the type of P. osborni was also referred to the latter species.
While it was the correct procedure to erect different species for the carapace and the abdomen as long as the parts had not been found connected in the same specimen, our larger collection of individuals in various growth stages and states of preservation leaves no doubt that the types of both belong to one species, which must be named P. macrophthalmus, as the latter precedes the other in the original descriptions and is better characterized by being based on a carapace. Professor Whitfield's accurate drawings show all essential features of the type specimens of P. macrophthalmus. We may add that Hall's figure 6, plate 80A, which is described as "a fragment of a crustacean associated with the E. remipes at Waterville, the relations of which have not been determined" is the broken fixed ramus of the pincers from a young individual of P. macrophthalmus.
Pterygotus macrophthalmus is quite distinct in its characters from all the European species. It is closely related to P. anglicus, in the similar form of the telson, but it is readily distinguished from the British type by characters of its own. One of these is the fishhooklike form of the extremities of the chelae and the different direction of their teeth. These features, at least the form of the distal ends of the chelae, are approached by P. osiliensis, a species with widely different telson.
Pterygotus atlanticus nov.
Plate 79, figures 3–5
Pterygotus sp. Whiteaves. Canadian Naturalist. 1883. 10:100
Remains of Pterygotus recorded from several Devonic horizons of eastern Canada have been briefly referred to on a previous page.
Billings, in Logan's Geology of Canada, cited their occurrence at Cape Bon Ami, Gaspé; the single specimen, however, proves to be not from the Bon Ami beds, but from the higher or Grande Grève limestone of the Lower Devonic. This specimen is a fragment of two abdominal segments, together having a length of 75 mm and covered with closely crowded, very coarse scales curved into the arc of a circle. It indicates a species of rather commanding dimensions. Sir William Logan also reported the presence of Pterygotus remains in the Gaspé sandstone, though these were described by Dawson as plants of the genus Selaginites [op. cit. p. 399]. Remains of Pterygotus have also been found in the lower marine Devonic Dalhousie beds of Dalhousie, N. B., in fragments which appear to have been washed seaward of their proper sites. Near Campbellton, N. B., in indurated limestones containing fish remains of probable Upper Devonic age, are also such remains, which were first noted by Whiteaves when describing the fish fauna of this locality.
Fragments, presumably of Pterygotus, have been reported from the Lower Devonic[7] of the Knoydart formation, Arisaig, Nova Scotia, where they are associated with fish remains of the genus Pteraspis and Cephalaspis.[8]
All of the occurrences referred to have been more or less particularly noticed by Clarke in Early Devonic History of New York and Eastern North America, but only that at Campbellton has furnished material adequate for description. This original material consists of a suite of three specimens, now in the Victoria Memorial Museum at Ottawa. These are a free chela, the coxa of a swimming leg and a small portion of a metastoma bearing traces of ornamentation. The chela is of slender form, straight, tapering regularly to the apex which is not preserved. The length is 50 mm, its proximal width, not counting the articulating process, is 9 mm, its distal width, at the point of fracture, about 3 mm. The ramus is but little compressed, its section irregular and convex, the greatest thickness being near the inner edge, whence the ramus abruptly narrows down to the dentate edge, and more gradually to the outer edge. The teeth are in two series, one of more numerous small sharp points, and one of larger distinctly furrowed teeth, the two series, however, not being sharply separated, and the larger series being surpassed by one tooth of much greater dimensions. The coxa indicates a large specimen; its manducatory edge is 38 mm long and bears a series of 13 stout, blunt teeth. The other specimen is probably a fragment of the posterior half of the metastoma, with its counterpart, showing the characteristic semicircular scales of Pterygotus.
These fragments point to a species of considerable dimensions, and all bear a distinct similarity to the corresponding parts of the giant Pterygotus anglicus of the British Old Red sandstone. There is still a differential element present in the regular tapering of the chela and the presence of a greater number of smaller teeth in the American type, both features recalling P. bilobus. As the Devonic beds at Campbellton are believed to correspond in their facies and age to the Old Red sandstone of Europe, the similarity with P. anglicus is quite suggestive. Probably with larger collections this species may prove to be a vicarious form of the British type.
Pterygotus buffaloensis (Pohlman) emend.
Plate 57, figure 3; plates 67, 68, 72–80
?P. cummingsi Grote & Pitt. Buffalo Soc. Nat. Sci. Bul. 1877. 3: 18, fig. 1
P. buffaloensis Pohlman. Ibid. 1881. 4: 17, fig. 1–3
P. sp. (cummingsi?) Pohlman. Ibid. p. 18, fig. 4
P. acuticaudatus Pohlman. Ibid. p. 42, pl. 2, fig. 3
P. quadraticaudatus Pohlman. Ibid. p. 43, pl. 3, fig. 1
P. ?sp. Pohlman. Ibid. p. 44, pl. 3, fig. 2
P. macrophthalmus? Pohlman. Ibid. p. 44
P. buffaloensis Pohlman. Ibid. 1886. 5: 24, pl. 3, fig. 1
P. bilobus (Huxley & Salter) Pohlman. Ibid. p. 27
P. buffaloensis, quadraticaudatus, cummingsi Laurie. Roy. Soc. Edinburgh Trans. v. 37, pt 2, 1893, p. 515, 517
P. buffaloensis Semper. Beitr. z. Pal. u. Geol. Oesterr.-Ung. u. d. Orients. 1898. 11:74 et seq.
P. buffaloensis Clarke. Zittel-Eastman, Textbook of Pal. v. 1, pt 2, 1900, p. 678, fig. 1425
P. buffaloensis Seeman. Beitr. z. Pal. u. Geol. Oesterr.-Ung. u. d. Orients. 1906. 19:51 et seq.}}
The quarrying operations in the cement rocks near Buffalo have brought to light numerous fragments of large Pterygoti which, as they were found, were described as new species by the curators of the Buffalo Museum. Seven species were thus named. Later years have furnished more complete specimens and these show that only two species of Pterygotus can at best be recognized at this locality.[9] One of these is identical with Hall's P. cobbi; the other a form of gigantic proportions, is here discussed.
The history of this species, briefly stated, is as follows:
In 1875 Grote and Pitt described and figured the masticatory edge of a gigantic coxa [pl. 79, fig. 1], which they termed P. cummingsi, stating that "P. macrocephalus (sic) and P. osborni are evidently very much smaller species, measuring scarcely as many inches as P. cummingsi does feet, and are undoubtedly distinct."
Then Pohlman in 1881 described and figured the swimming leg here reproduced on plate 78, figure 2, as representing his new species P. buffaloensis, referring also a fixed ramus of a large chela to the same species. The latter is identical in form with the same part of a much smaller individual figured by Hall on his plate 80A, figure 6 as "undetermined crustacean." The following year Pohlman published a further paper on fossils from the waterlime group of Buffalo in which a telson of a young individual slightly more slender than the average telson is made the type of a species, P. acuticaudatus, and a detached ultimate postabdominal segment that was mistaken for a telson is used as basis of a species named P. quadraticaudatus. In regard to this telson we may say that there appears to have existed some variation in form, as there is among our specimens one showing the other extreme, namely, a relatively broad form [pl. 72, fig. 3]; none of these differences seems sufficient for the erection of new species, since the occurrence of transitional stages is obvious. Moreover, a slight lateral compression which clearly has affected some of the specimens, and specially the type of
 |
 | |
| Figure 72 Original figure of Pterygotus cummingsi Grote & Pitt | Figure 73 Pterygotus buffaloensis Pohlman. The original figures |
acuticaudatus, is fully competent to produce a like effect [pl. 77, fig. 5]. Text figure 75 is a reproduction of the type of P. quadraticaudatus and plate 76 shows the ultimate segment, which in reality it is, in position in a nearly complete postabdomen. Finally Pohlman cited P. bilobus Huxley and Salter, as among the forms of the waterlime at Buffalo, basing his assertion on a fragment consisting of eight posterior segments. This fragment is preserved in the museum of
 Figure 75 The type of P. quadraticaudatus redrawn. Natural size |
 |
 | |
| Figure 74 Original figure of Pterygotus quadraticaudatus Pohlmann | Figure 76 Type of Pterygotus bilobus Pohlmann redrawn. Natural size |
As it would be fatuous to base a species on the manducatory edge of a coxa or even the whole coxa itself,[10] Grote and Pitt's term cummingsi is here rejected. This is the more necessary, as these authors afterward referred to their species the free ramus of a chelicera which is clearly identical with P. cobbi Hall.
Pohlman's P. buffaloensis, acuticaudatus, quadraticaudatus, macrophthalmus (?) and bilobus all belong to one species. We adopt the first name here used, P. buffaloensis, emending the species by a fuller description.
Description. Body slender, lanceolate in outline, five times as long as wide.
Cephalothorax. The carapace in mature specimens is trapezoidal, the lateral margins subparallel, slightly convex or angular, forming an obtuse angle with the slightly convex anterior margin. The posterior edge is broadly concave. The surface seems to have been uniformly convex. The compound eyes form the antelateral angles of the carapace, are subelliptic in outline and equal about one half the length of the carapace in younger and four ninths in the largest individuals.
The ocelli and the doublure are as in P. macrophthalmus.
Abdomen. The abdomen does not differ in either its proportions or characters from that of P. macrophthalmus. The operculum which is not well known in the latter, is here well exposed in several specimens. It does not differ materially in form from the same part in the British and Russian species. It is longer than any tergite, its length being one fourth of the width; and its posterior margin has, as pointed out by Woodward, the form of a bracket, while the anterior margin is gently concave and the lateral margins run obliquely forward and inward, the anterior angles being distinctly rounded away.
The transverse line of the operculum, which has hitherto been observed only in Eurypterus, is quite distinctly seen near the margin of the right half of the operculum and can be traced to about one half the distance to the median suture.
The four following sternites are readily distinguished from the tergites by their greater length and the round sweep of their lateral margins. The antelateral angles have not been seen in our specimens on account of the strong overlap of the sternites which must have amounted to fully one half the length of the plates. The doublure of the posterior margin is narrow. The median suture is visible in the operculum and the next sternite. In specimen plate 77, figure 3, the third sternite has split with a straight cleft, thus indicating a line of weakness where the suture might be expected. The doublure of the posterior margin is narrow, amounting to only one fifth of the exposed part of the sternite [pl. 72]; and in the operculum it seems to have been reduced to a narrow band but 1 mm wide in mature specimens. The lateral doublure is well seen on the left side of the specimen; it attains the width of the posterior doublure in its postlateral angle but narrows so rapidly that it does not reach the antelateral angle.
Postabdomen. The postabdomen of this species exhibits the features of that of P. macrophthalmus with the exception of the ultimate segment which in mature individuals [pl. 76] abruptly flares out, at one fourth its length, into rounded wings that increase the width of the segment by one fourth. The edge of these alae is coarsely serrate.[11] The median line of the dorsal side is likewise marked, in the middle third of its length, by a keel and covering of massive scales.
The telson is very broadly obovate to circular in outline. It surpasses the ultimate segment in length and in width by one third. The character of the marginal serrations is as in P. macrophthalmus; and as in the latter, the telson possessed a median axis or thickening which here is equipped on the dorsal side, with large spines [pl. 73, fig. 2].
Appendages. The form of the epistoma could not be made out in this species.
Some of the preoral appendages or chelicerae are so admirably preserved as to shed light on the structure of these organs and to decide the much disputed number of their segments and the character of the basal attachment. These appendages were long and very powerful, their length equaling fully one half that of the body without the telson. The first segment is subcylindrical, about eight times as long as wide in the compressed state; contracted in the basal seventh of its length, and very gradually expanding toward the distal end. The next segment, which with the third forms the vicious looking pincers or chelae, is of about equal length with the first and easily revolved on it with a rounded basal articulating surface. The basal third of the second segment is inflated, evidently to receive the strong muscles operating the free ramus. Both rami are nearly straight or slightly convex outward, tapering toward the tip and relatively slender. Their distal parts are not roundly curved as in P. cobbi and the British species, P. anglicus and bilobus, but end in a sharp distal point and each carries a terminal tooth directed slightly inward, resembling in this structure the jaws of P. osiliensis. The fixed ramus carries on the proximal half an irregular series of teeth directed obliquely forward, and on the distal half, smaller teeth that stand vertically. One or several of the oblique teeth surpass all others in length and extend daggerlike into the cavity between the jaws. They are finely barbed on the inner margin, a feature not observed in any congeneric species. The barbs are quite distinct in specimen, plate 77 figure 3 and still better shown in the fragment reproduced in plate 74, figure 5. They are broad and low near the point of the teeth and become sharp and narrow near its base. Between the larger teeth more numerous and much smaller denticles are everywhere intercalated. The movable ramus carries in its basal part two (in the younger) or three (in the older individuals) stronger teeth directed forward and an irregularly alternating series of mostly smaller teeth on the other parts. The latter all stand vertical in the jaw. One of them surpasses the others in length and is flanked by a group of teeth of about half its length. The edges of these are smooth. All teeth are longitudinally striated. The specimen, plate 77, figure 3, shows apertures near the base of the teeth on the movable ramus.
The walking legs or endognathites are not very well displayed in our material; and the basal segments fail in all save one specimen [pl. 57, fig. 3]. In the latter the coxae even retain the epicoxites in position, the only case observed in the entire eurypterid material at our disposal. The coxa is slender, with a sigmoidal curvature and the manducatory edge carries a series of about nine teeth. The first two segments appear to be short, ringlike. The legs are slender and relatively longer in this species than in most of its allies, attaining twice the length of the cephalothorax; smooth, cylindrical and tapering regularly toward the blunt spine forming the last joint. The middle segments were longer than both the basal ones and the last. The four pairs do not seem to have differed materially in length.
The swimming legs were relatively slender and small extending but little beyond the posterior margin of the third tergite in the older. The coxa is of enormous size in relation to the remainder of the leg. It is half as long as the latter, less the small paddle, and its expansion covers half the underside of the carapace [pl. 78, fig. 2]. Its principal part is rectangular in outline, the interior and posterior sides nearly straight and the others convex, the outer side having a deep sinus in the middle for the articulation with the next segment. The gnathobase is a strong trapezoidal lobe connected by a contracted neck with the main body of the coxa. On the inner or slightly curved edge, it bears 13 relatively blunt teeth which decrease in size posteriorly with a slight backward direction. The first tooth is distinctly the largest and diverges from the others, and the last teeth at the posterior end (the 14th and 15th of the other species) coalesce into a rounded lobe. The circular opening near the posterior
 Figures 77, 78 Pterygotus buffaloensis Pohlman. Outline sketches of swimming legs. Figure 77, ventral view; figure 78, dorsal view |
border of the coxae which occurs in Limulus, Eurypterus and Hughmilleria, has not been seen in Pterygotus.
The second segment is short and ringlike, broadest on the posterior side and provided with a concave outer margin. The third appears wedgelike and is broadest on the anterior side; the fourth is again ringlike, broader than the preceding segment and broadest on the posterior side. The fifth segment is quite like the corresponding part in P. osiliensis, triangular semioval in shape, the anterior margin the longest and the distal margin deeply notched; the sixth segment is irregularly rhomboidal in form, its proximal margin furnished with a strong process that fits into the corresponding notch of segment five, forming a strong articulation, and its distal margin is produced bluntly to articulate with the seventh segment. The latter is the largest one in the swimming leg after the coxa. Its longest edge equals in length the preceding five segments. It is oval in form, as in other species, flat and expands toward the distal end. Its proximal margin is bilobed for articulation with the sixth segment and its distal margin is bluntly indented in the middle for the articulation with the next segment. The outer lateral margin is slightly convex, the inner nearly straight. Both are thickened to strengthen the bladelike expansion. The distal portions of the lateral margin are distinctly serrate. The rather large triangular process of the inner side of the distal margin is, as in the other eurypterids, set off from the rest of the segment by a straight suture. The eighth (paddle) is a little shorter than the seventh, but markedly more slender; it is long, ovate, with lanceolate distal part. Its inner lateral margin is coarsely and its outer margin finely, serrate. The single perfect paddle of our material carries at its distal end a distinct disklike "terminal palette."
The metastoma is elongate cordate; its greatest width about one third the length from the anterior margin. The width equals three fifths of the length. The posterior extremity is well rounded in some specimens and apparently truncated in others. The "Umschlag" or doublure of the inner face, is distinctly seen in one of the specimens [pl. 77, fig. 1] and the wrinkling caused by the compression of the membrane is visible in the figure. In some specimens [pl. 78, fig. 4] a deep median furrow or cleft extended about one third of its length. The inner face was smooth, the outer sculptured as described below.
The epistoma has not been observed. The endostoma was, however, observed lying under a metastoma and accidentally turned backward [pl. 78, fig. 4]. It closely resembles in form the endostoma of Eurypterus fischeri. It is a thin suboval shield with deeply emarginate anterior margin. Its lateral and posterior boundaries are ill denned, as it there was connected or gradually passed into the thin ventral integument of the cephalothorax. The inner margin of the frontal notch is thickened and a median thickening proceeds from it, posteriorly ending in a thickened semioval plate.
The opercular appendages of only two specimens have been observed. These represent the female appendages of young examples. The best preserved and oldest specimen gives two aspects of the appendage, the exterior on the mold of the fossil, and a partially interior one on the cast. Both together show that the appendage was broadly hastate at the anterior end, extending to nearly the anterior margin of the operculum and was produced posteriorly with a clublike process which, in the young individuals at least, did not extend beyond the posterior margin of the operculum. This process was overlapped on both sides by the inner margins of the two opercular plates, which left only the narrow median portion exposed.
In the largest of the specimens, a distinct sigmoid vermiform depression is seen to proceed on one side from the anterior end of the appendage, passing just within the anterior margin of the opercular plate for some distance and finally swinging backward, gradually tapering toward its extremity. This depression corresponds in location and form to one of the paired horn-shaped organs observed by Holm in E. fischeri on the inside of the operculum on either side of the opercular appendage. It could be well conceived that its presence prevented the filling of the space with mud for a time and its final collapse produced the depression. The opposite opercular plate is bent over and crumpled so that this hornlike organ is not there observable.
Sculpture. The sculpture of the carapace consists only of fine tubercles which are most distinct and closely arranged along the margins and between the eyes; that of the remainder of the integument is composed of linear, crescentlike or angular scales.
The scales of the tergites are small, mostly linear or flat crescentic and distributed on the anterior half of the tergites. The sternites are entirely covered with large, prominent scales except in a belt along the posterior margin that corresponds to the doublure. The anterior region is covered with small linear or bean-shaped scales which in posterior direction become first crescentlike and then angular, increasing at the same time in size and decreasing in distinctness.
The coxae of the swimming legs bear small, widely distributed crescentic to circular scales that are directed outward. The other paired limbs show small crescentic scales on the basal segments and longitudinal lines of sharply angular scales on the distal segments.
The metastoma and the hastate part of the female opercular appendage are also provided with crescentlike scales.
On the sternites the scales become smaller, but very densely crowded, more prominent, and show an ever increasing tendency in posterior direction to become circular. The last tergite is covered on its anterior half with strongly raised, evenly distributed, black, round tubercles. Similar small circular scales are also observed near the anterior margin of the telson which otherwise is smooth.
Measurements. As we have at our disposal only two complete specimens, and these represent but immature individuals, the measurements of the mature specimens have been obtained by a series of proportions. We give first the measurements of specimen, plate 72, which is the best preserved of the complete individuals.
| Millimeters | |
| Length of carapace | 39 |
| Width | 52 |
| Length of largest tergite | 25 |
| Width | 60+ |
| Length of last postabdominal segment | 26 |
| Width | 40? |
| Length of telson | 39 |
| Width | 41 |
| Total length of specimen | 290 |
| Length of chelicera on counterpart | 115 |
| Length of chela | 26 |
| Length of walking leg beyond margin of head | 67 |
| Length of swimming leg beyond margin of head | 60 |
| Largest carapace observed: | Centimeters | |
| Width | 11.5 | |
| Length | 8.8 | |
| Length of lateral eye | 4 | |
| Largest coxa observed: | ||
| Length of anterior edge | 20 | |
| Length of manducatory edge | 8.2 | |
| Largest metastoma: | ||
| Length | 7 | |
| Width | 4.2 | |
| Largest tergite: | ||
| Length | 10 | |
| Width about | 37[12] | |
| Largest telson: | ||
| Length | 11.5 | |
| Width | 11 | |
The size of the largest tergite and coxa suggests that this species reached truly gigantic dimensions for merostomes and rivaled the British P. anglicus which Woodward [loc. cit. p. 43] felt justified in concluding "attained a length of six feet, and a breadth of nearly two feet, at the widest part of its body." From the relative length and width of the tergites in our specimens we infer that P. buffaloensis was more slender than the British species. The largest tergite leads us to the conclusion that it belonged to an individual 1.65 m or 5 feet, 5 inches long. The very large base from the waterlime at Buffalo [pl. 79, fig. 1] must by comparison of the length of its manducatory edge with that of other specimens, have been the formidable masticating organ of an individual not less than 2 m (2.01 m) or 6 feet, 7 inches long.
The waterlime has furnished the chelae of still another gigantic eurypterid, that of P. cobbi. As the relative dimensions of the chelae to the other parts of the body are approximately uniform in the other species, we infer from their size (13 cm) that it also attained 5 feet in length.
Pterygotus buffaloensis and P. cobbi vastly surpassed all other arachnids or any organisms of our Upper Siluric era in size and armed with their powerful prehensile pincers, and being evidently active swimmers, as shown by their large swimming legs and telson, they must have been the terrors of the waterlime sea.
Remarks. The principal differences in P. buffaloensis and the closely related P. macrophthalmus are in the form of the carapace, which is less rounded, but more trapezoidal in outline, the frontal margin being less evenly convex; and in the form of the ultimate segment and telson. The telson of the former is not elongate obovate as in P. macrophthalmus, but broadly ovate [pl. 72, fig. 1; pl. 73, fig. 2]. While that of P. macrophthalmus is about one sixth longer than wide, that of P. buffaloensis is as wide as long or sometimes even wider [pl. 72, fig. 3]. Corresponding to this remarkable width of the telson, the preceding, ultimate, segment of the postabdomen is also much wider in P. buffaloensis than in P. macrophthalmus, the widening taking place rather abruptly near the middle of the segment.
Pterygotus cobbi Hall[13]
Plate 77, figure 6
Pterygotus cobbi Hall. Palaeontology of New York. 1859. 3:417*, pl. 83B, fig. 4; pl. 84, fig. 8?
Pterygotus cummingsi Grote & Pitt. Am. Ass'n Adv. Sci. Proc. 1878. 26: 300, 301, fig. 1
Pterygotus cobbi (P. cummingsi) Semper. Beitr. z. Pal. u. Geol. Oestr.-Ung. u. d. Orients. 1898. 11: 80
This species is based on the "free ramus of the chelate appendage." The type, a rather poorly preserved specimen, is from the waterlime at Buffalo and now in the American Museum of Natural History. Hall also doubtfully referred to this species a postabdominal segment characterized by rather evenly distributed small triangular scales. In form and surface sculpture this is identical with the segment of the postabdomen of Eusarcus scorpionis and quite obviously to be referred to that species. The ramus, however, is distinct from that of the chelae of both P. buffaloensis and P. macrophthalmus in the greater relative width of its base and its more regular tapering in distal direction; and most strikingly by the even rounding of the distal end to form a terminal tooth instead of an angular extremity.
By a strange coincidence, this type which Hall says was the "fifth unequivocal fragment of the genus Pterygotus that came under [his] notice from any American locality," seems to represent the rarest of all forms; for so far as we know only one other representative of this species has been thus far found. This is a ramus about twice as large as Hall's type. Grote and Pitt figured it and referred it to their species P. cummingsi, which had been previously described and based upon a coxa. The latter probably belongs to P. buffaloensis, while the ramus is not referable to that species. These writers cited as distinguishing characters from P. cobbi, the difference in size and the fact that the "apex of the joint is pointed in P. cummingsi, while in P. cobbi and P. anglicus it is obtuse." By the "apex of the joint" the point of the terminal tooth is meant. The type of P. cobbi, however, has only obtuse teeth and it is obvious that this is entirely due to weathering. To the same cause and the poor preservation of the type in general may be also attributed the absence of the smaller intercalated teeth in both specimens.
The question suggests itself whether old age could not have produced in P. buffaloensis or P. macrophthalmus a free ramus like that upon which this species is based; or whether it might not be indicative of a slight variation only. The first suggestion is refuted by the presence in our collection of free rami of buffaloensis of similar size, with typical angular points of the jaws; and perhaps still more by the fact that the European species P. bilobus, P. anglicus and P. barrandei, which possess similar rounded free rami and have afforded the entire chelicerae, also demonstrate that the fixed ramus is correspondingly formed, and that these characters of the chelicerae appear even in younger individuals. We insert here a sketch of the chelicera of P. barrandei, whose free ramus possesses the greatest similarity to that of our type, in order to show the probable form of the entire chelicera of P. cobbi.
 Figure 79 Pterygotus barrandei Semper, here introduced for comparison. Natural size. (From Seeman) |
The second suggestion, above advanced, that P. cobbi may be only a variety, is also refuted by the evidence from the European material, which demonstrates that the chelicerae are very good indicators of specific distinction. The chelicerae of the P. buffaloensis-macrophthalmus group are almost identical with those of P. bohemicus Barrande, while those of the associated P. cobbi correspond closely to those of P. barrandei Semper, found with bohemicus in the Bohemian Upper Siluric stage.
We are thus convinced that P. cobbi, although represented only by a free ramus, deserves recognition as a separate species. Its full characters will have to be established by future discoveries. For the present we base the description on the better preserved second specimen.
The main body of the ramus is nearly straight, its outer edge slightly convex, the inner slightly elevated in the middle in support of the largest tooth. It tapers uniformly, diminishing in width from the articulating extremity to the base of the terminal tooth by one half. It bears three series of teeth, one, consisting of the largest (four in this specimen) and culminating in the second tooth, and another only half as long, intercalated between the large teeth. A few teeth of a third order again half as long as those of the second order are noticeable near the basal part of the ramus.
The teeth possess a very slight forward curvature and stand at right angles on the jaw with the exception of those of the second order near the base, which correspond to the oblique direction of that part, and are directed forward. Fine longitudinal lines are noticeable on the teeth. The distal end of the ramus curves somewhat abruptly into a tooth, longer by one fourth than the culminating tooth of the middle part of the ramus and subparallel to it.
The length of the ramus is 13 cm (5⅛ inches). Its width at the base is 16.8 mm. The culminating tooth measures 19.4 mm.
If we assume that this ramus possessed the same proportional size to the length of the body as in other members of the genus, we derive an individual 6 feet, 7 inches long. Whatever the actual dimensions of this eurypterid may have been, the size and aspect of the jaw are convincing proof of its formidable character.
Pterygotus (Erettopterus) globiceps nov.
Plate 82, figures 1–12
Eurypterus maria (in part) Clarke. N. Y. State Mus. Bul. 107, pl. 2, fig. 3
The presence of a true Pterygotus in the Otisville fauna is shown by several carapaces, a few body segments, a swimming leg and several telsons. As no entire specimen has been obtained, we are not in position to say whether all these parts belong to but one or to several species. We have referred them provisionally to one species since the carapaces do not exhibit differences of sufficient importance to base distinctions upon, though they undoubtedly represent different growth stages. We have selected the largest and most perfect carapace [pl. 82, fig. 6] as the type and derive from this the following description:
Description. Carapace approaching a circle in outline, with a posterior segment cut off, so that the length is one fifth shorter than the width. The greatest width is in the anterior half, just behind the eyes. The frontal margin and the greater portion of the lateral margins form a continuous subcircular curve, the posterior fourth of the lateral margins slightly concave and the posterior margin nearly straight. The postlateral angles are approximately right ones. A narrow flat margin with a thickened rim surrounds the carapace except where the eyes are situated where it is presumably continuous and turned under. This margin widens near the postlateral angles. The posterior margin is also furnished with a narrow flat border. The carapace appears to have been quite convex before compression. The eyes are very large (one half the length of the carapace), of elliptic outline, hardly projecting, and situated at the well-rounded antelateral corners. Traces of the facets are noticeable. The surface is ornamented with contiguous, low broad tubercles. The first tergite is very short (11 times as wide as long), its posterior margin concave in the middle, the lateral margins rapidly diverging and curved. The surface exhibits the same ornamentation as the carapace.
Several tergites have been observed of a Pterygotus exhibiting the same typical Pterygotus-sculpturing as the carapace of this species, though more pronounced. One of these, with much extended lateral "ears" is reproduced on plate 82, figure 8. Some fragments indicate that this species attained the gigantic proportions of the Bertie waterlime species and that the smaller forms are but early growth stages. The relatively very great size of the lateral eyes points to the same conclusion.
The swimming leg [pl. 81, fig. 10] agrees with the corresponding organ of its allies in its smaller elongate paddle and long seventh segment.
Metastomas and telsons, referable to Pterygotus, have also been observed in the Otisville beds. The latter are of bilobed form and indicate Huxley & Salter's genus Erettopterus. The half of one telson, obviously too short, through anteroposterior compression shows a fringe of very minute, acute points such as have, to our knowledge, not been observed before on the telson of a Pterygotus. Smaller specimens (as that reproduced in plate 82, figure 12) are better preserved and consist of elongate bilobate bodies with a central, posteriorly tapering, raised axis. The lobes are broad and well-rounded.
While the carapace of this species strikingly resembles that of P. (Erettopterus) bilobus Huxley & Salter [see especially Woodward, 1869, pl. 10, fig. 3] in its subcircular outline and larger eyes, the telsons from Otisville are much shorter and less bilobed and can be only compared to those of P. (Erettopterus) banksii [Huxley & Salter, Monogr. pl. 12, fig. 23, 36, 37]. Both carapaces and telsons thus show closest relationship to species of the subdivision Erettopterus, a fact that argues for the union of the carapace and telsons.
Ontogeny. By far the most interesting part of this small series of specimens are the four immature individuals [pl. 82, fig. 1–4] which give us the first information on the ontogeny of a Pterygotus. Of these four two are clearly in a larval condition and represent the nepionic stage, while the others have certain characters in common which, together with their size, support the view that they are still immature and belong to the type intermediate between the nepionic and ephebic conditions.
The two nepionic specimens are characterized above all by the relatively great size of the carapace, the small size of the abdomen and small number of segments. The carapace occupied nearly one third the length of the whole body while in the mature P. macrophthalmus, the only species of which we have whole individuals, it reached only about one eighth the length of the body. The fourth figure indicates how far in the neanic stage the body had overtaken the carapace in growth. We judge that in this individual the carapace was not longer than one fifth the entire body. The carapace of the nepionic stage is also wider than any other part of the body, the latter tapering directly from the base of the carapace to the tail.
The imperfection of the body is very apparent in the first individual, which probably had no more than six or seven segments and the next but eight or nine without the telson. The segments are all of equal length, but diminish rapidly in width, while in the mature Pterygotus they gradually widen to the fourth and thence again very gradually contract to the telson.
The compound eyes are, in contrast to the nepionic stages of the other eurypterids, not relatively larger than in the ephebic stage, but rather smaller. This peculiar difference is quite apparently due to the fact that the mature Pterygotus has relatively larger compound eyes than the other genera and we may infer from this relation of the nepionic to the ephebic eyes, that the large eyes of Pterygotus are a further development of a feature larval in the whole class. While the nepionic eyes were not relatively larger than those of the mature individuals they seem to have been somewhat more prominent or bulging. The first of the nepionic specimens [pl. 81, fig. 1] exhibits two very distinct tubercles near the anterior margin which, if ocelli, would have a position corresponding to that in the embryo of Limulus polyphemus.
The telson of the nepionic stage has unfortunately not been seen. We surmise that it would give interesting clues as to the development of the bilobed telson characteristic of Erettopterus.
The specimen figure 2 exhibits a distinct cleft or rupture, slightly more irregular and curved than figured, extending over the posterior part of the carapace and the following segments. This may be the result of molting. Considering the small size (1.5 mm) of the specimen, it is quite possible that this was the first molt after hatching.
The neanic stage is represented by the two specimens figures 3, 4. The specimen figure 3 has suffered strong compression in anteroposterior direction and is therefore not competent to indicate the form of the carapace in this stage, but it corroborates the evidence from the other as to the relatively increased size of the compound eyes and the distinctness and position of the ocelli.
The carapace has lost its position as the broadest part of the body, the preabdomen having been completed and become the widest portion. In other growth-stages of eurypterids obtained at Otisville, the postabdomen is completed before the preabdomen, and it is hence to be inferred that in the specimen figure 3 the number of segments is complete. This is also suggested by the presence of a narrower first preabdominal tergite such as is found in the mature stage.
The compound eyes are relatively larger than in the nepionic stage, occupying fully one half the sides of the carapace, but less prominent. The compound eyes of the first specimen are especially notable for the distinctness with which a thickened ring is seen to surround the inner side of the eye. The same is already visible on the second nepionic specimen figure 2 and partially noticeable on the type. It probably surrounded the whole eye and its function was apparently to support the prominent cornea, corresponding in that to the orbital ridge in Stylonurus excelsior.
| Measurements. | |
| Type, carapace, length, 12.3 mm; width, 15.5 mm | |
| Length of first tergite, 1.5 mm | |
| Width of largest tergite observed [pl. 82, fig. 8], 25.5 mm | |
| Length of same, 9.9 mm | |
| Largest telson observed [pl. 82, fig. 11], length (incomplete), 35 mm; width (restored), 60.2 mm | |
| Smaller telson, width, 7.4 mm; length, 7.7 mm | |
| Smallest specimen, length (incomplete), 1.6 mm; width, .8 mm | |
Horizon and locality. Rare in the Shawangunk grit at Otisville, N. Y.
Pterygotus (Erettopterus) grandis (Pohlman) emend.
Plate 81
Ceratiocaris grandis Pohlman. Buffalo Soc. Nat. Hist. Bul. 1883. 4: 19, fig. 5
The waterlime at Buffalo has furnished the broad symmetrical remains of a creature described by Pohlman as the carapace of a gigantic Ceratiocaris on the assumption that the two semicircular valves of this supposed phyllocarid had been spread out on both sides of the dorsal line. This view is clearly erroneous and the fossil is the telson of a Pterygotus. According to Pohlman it was found in the same bed which yielded the Pterygotus. The specimen represents the section with bilobed telson (Erettopterus). 
Figure 80 Original figure of Ceratiocaris grandis Pohlman Pterygotus banksii, a British Ludlow form, possessed a similar telson [Huxley & Salter, Monogr. pl. 12, fig. 45] although it is considerably surpassed in transverse development by this American species.
As a telson this fossil is characterized by the anterior transverse hinge line where it is connected with the preceding segment, the man smooth antelateral edge and the scalloped postlateral edge. The anterior half is provided with a median ridge while the posterior part is divided by a median cleft. It is probably the character of this median line which led to the reference of the fossil to Ceratiocaris.
The form of the telson is transversely elliptic with rather acute ends. Its major diameter, 24 cm, is to the minor as 12 : 7. The anterior hinge line is but 69 mm long, thus indicating the broad flaring character of the telson in comparison to the postabdomen. The scallops are broad and shallow; at the termination of the median line is a deeper and broader emargination. The sides of the median cleft are curved outward and overlap considerably. The surface is very finely granulated.
This telson must have been the effective propelling organ of a gigantic merostome, which was undoubtedly 5 feet or more in length. In view of the fact that the known fragments of Pterygotus cobbi, from the same locality and formation, also represent a colossal animal, it is possible that the rami of P. cobbi and the telson of P. grandis will prove to belong to the same animal.
Pterygotus monroensis Sarle
Plate 70, figures 3–5
Pterygotus monroensis Sarle. N. Y. State Palaeontologist Rep't. 1902. p. 1102, pl. 24, fig. 7, 9
?Pterygotus sp. Sarle. Ibid. p. 1104, pl. 24, fig. 6, 8
Sarle describes this species as follows:
This species is founded on a single specimen, a cephalothoracic shield. The outline of this shield is semielliptic with the posterior edge noticeably incurved. The surface is moderately convex, and along the sides and front is a threadlike border. The length of the shield, without the genal angles, is 30 mm, with them 37 mm; the breadth at the base 38 mm. The compound eyes are prominent and project beyond the outline of the shield. They are subelliptic. with a distinct angulation on the inner side of each, produced by an indentation of the inner anterior part. They are 14.5 mm long and 6 mm wide. The facets can be made out with a good magnifying glass. The eyes are located a distance equal to their own length from the front of the shield and 27 mm from each other. A line connecting their bases cuts the axial line a little back of the center of the shield. The ocelli are on a small tumescence just back of this. The ornamentation is almost obliterated, but can be made out at one point, where it consists of minute, short, flat, lobelike scales.
Its differences from P. macrophthalmus are also indicated by the author as follows:
The cephalothorax of this new species differs from that of P. macrophthalmus in that its length is nearly equal to its breadth; the compound eyes are over one third the length of the shield, elongated, angulated on the inner side, situated farther back, and separated by nearly twice their length. In P. macrophthalmus the length of the shield is three fourths the breadth; the eyes are about one third the length of the shield, anterior, globular and separated by a distance about equal to their length.
The type specimen, which is in the State Museum, possesses some characters quite suggestive of a more proper reference to Hughmilleria. Sarle remarks that the form of the eyes suggests those of "P. bilobus Salter and P. banksii Salter and also those of H. socialis." The reference to Hughmilleria in this connection appears to us especially significant, since the eyes show the distinct angulation on the inner side, so characteristic of that genus, and moreover fail to exhibit any signs of the facets, generally quite distinct in Pterygotus. It is quite possible that this specimen is a very large carapace of Hughmilleria partly doubled upon itself in front (of which there is evidence along a break); although on the other hand it must be conceded that the lateral eye is relatively larger than that of H. socialis.
So far then as concerns this carapace P. monroensis is an uncertain species, but unmistakable evidence of the presence of a true Pterygotus in the Pittsford shale is afforded by the free ramus of a chela,[14] reproduced in plate 70, figure 3. Sarle has separated this and a metastoma[15] [pl. 70, fig. 4] on the ground that they belong to coarse-scaled fragments that represent another species. Inasmuch as the carapace as a rule has a much finer sculpturing than the rest of the body (e. g. in P. macrophthalmus), there seems little ground to assume the presence of more than one species of Pterygotus in the Pittsford beds.
Judging from the ramus of the chelicera, this type was more closely related to P. cobbi than to any other form, the latter species possessing the same rounding of the extremity of the ramus and similar form and direction of the teeth [pl. 77, fig. 6], the latter being still a little more rectangular upon the shaft than in P. cobbi.
Pterygotus (Eusarcus?) nasutus nov.
Plate 86, figures 6–10
Description. Carapace pentagonal; one fourth wider than long, consisting of a greater posterior quadrilateral portion and a smaller triangular frontal portion; the lateral eyes occupying the anterior angles of the quadrilateral portion. The lateral margins are subparallel, gently convex, the frontal margin transverse for a short distance and bluntly angular in the middle; the posterior margin nearly straight transverse. The lateral eyes, about one third the length of the carapace, appear broadly triangular when partly folded under the carapace and compressed, but are normally subcircular and strongly project in the middle. Ocelli forward of center of carapace. Ornamentation small, crescent-shaped scales.
Horizon and localities. Frankfort shale (Schenectady facies) at Schenectady, Aqueduct and Duanesburg.
Remarks. This species is well characterized by the snoutlike frontal projection and the prominent antelateral angles with their large eyes. It does not appear to have reached the dimensions of the preceding species, the largest carapace being only 30 mm wide and 22 mm long. The type specimen is 9.5 mm long and 13 mm wide. Its lateral eyes are about 4.5 mm long.
Pterygotus prolificus nov.
Plate 86, figures 1–5
Description. Carapace semielliptic to roundish quadratic; length to width approximately as 4 : 5; frontal and lateral margins evenly convex, posterior margin straight transverse to gently concave. Lateral eyes large, one third the length of the carapace, elliptic in outline, marginal, situated in the antelateral corners, showing traces of facets. Ocelli subcentral in position. Ornamentation not observed.
Horizon and localities. Frankfort shale (Schenectady facies) at Schenectady, Aqueduct, Rotterdam Junction, Duanesburg, Schoharie Junction and the Vly creek. This is the most common eurypterid of the Frankfort shale; it is, however, possible that more than one species is comprised in this preliminary description.
Remarks. The outline of the carapaces is quite variable, at times being nearly quadrilateral [pl. 86, fig. 3], at others almost semicircular. Much of this diversity of form is obviously due to the compression and wrinkling of the rather flaccid carapaces in different directions, but in the best preserved specimens there is still an element of difference left after allowing for all the secondary influences that suggest the presence of more than the two species of Pterygotus here described and a distinction between the round and the squarish carapaces. This suspicion is strengthened by the evidence from the patches of integument showing patterns of ornamentation which also indicate a greater number of species of Pterygotus. We have selected the squarish specimens as typical of P. prolificus.
Disjecta membra of Pterygotus from the Frankfort shale
Besides the carapaces here used for specific diagnosis, many other fragments are referable to Pterygotus. The most characteristic of these may be briefly noted.
Plate 86, figure 19 represents a fragment of the arm of a pincer.
The distal end of a swimming leg, which in the form of the seventh and eighth segments resembles the leg of a Pterygotus more than that of any other genus, is reproduced in plate 86, figure 16. In the same group belongs plate 86, figure 20. There occur entire large swimming legs which probably belong to O. prolificus. Another very characteristic group of fragments are the female opercular appendages [pl. 87, fig. 1–3]. They resemble those of the giant P. anglicus and from their dimensions may belong to P. prolificus. Still another form of a large appendage corresponding to a type observed at Otisville, is seen in plate 87, figure 4. The most remarkable of the opercular appendages is one [pl. 86, fig. 11] which beautifully retains the characteristic broad overlapping crescent-shaped scales of the Pterygotus-Slimonia group. This resembles the male opercular appendage of Slimonia.
The metastoma reproduced in plate 86, figure 17, resembles in the anterior half, which alone is preserved, so much the metastomas of several species of Pterygotus and also corresponds in its large size so perfectly to the parts of P. prolificus that there is little doubt of its belonging with the large carapaces of that species.
Plate 87, figure 9 represents a fragment of a large tergite with traces of the Pterygotus ornamentation. This can be referred to P. prolificus with some certainty.
Characteristic telsons of Pterygotus [pl. 87, fig. 5, 7] are not infrequent at Schenectady and Duanesburg. A very different type is represented by plate 87, figure 8. It exhibits a peculiar ornamentation, consisting of small groups of tubercles on low nodes arranged in subconcentric lines; the other side was smooth. The serration of the margin is very distinct and shows by its direction that the small incision on the longer side is the middle of the posterior margin of the telson and is a faint beginning of the bilobation characteristic of Erettopterus.
Plate 87, figure 6 illustrates a form of fragments met with repeatedly in the beds at Schenectady, and quite obviously a last postabdominal segment best comparable to that of a Pterygotus.
Finally, these black shales also contain small patches of integument which retain the surface sculpture in a preservation surpassing any hitherto observed in our eurypterid-bearing rocks. Some of these patches [see pl. 86, fig. 11–15] are clearly referable to Pterygotus.[16]
- ↑ Pterygotus raniceps, also adduced for comparison by Sarle, has a more acutely triangular carapace and is here referred to Eusarcus.
- ↑ In discussing the resemblances between Eurypterus and Hughmilleria [ibid. p. 1090], Sarle correctly indicated the similarity of Hughmilleria to Eurypterus lanceolatus in the form of the carapace and the swimming arm.
- ↑ It also seems to be subject to considerable variation as evidenced by figure 4, plate 62, and figures 3, 4, plate 66.
- ↑ The next important difference is in the character of the spiniform walking legs. As in Pterygotus, these consist of seven joints, but the several pairs present a greater contrast to their respective lengths, are proportionately more robust, and each joint, from the third to the sixth inclusive, carries a pair of ventrally and distally articulated slender, curved spines. It is doubtful if any species of Pterygotus has spines on these appendages; certainly, in several species in which these limbs have been found apparently well preserved, they are lacking.
- ↑ The senior author follows Sarle in the preliminary description of the Otisville fauna in seeing in the larger preoral appendages and the marginal eyes the critical differences between Hughmilleria and Eurypterus.
- ↑ It is drawn too coarse on the original figures here reproduced and would hardly be noticeable in natural size drawings.
- ↑ The Knoydart formation, so named by Ami, is regarded by Fletcher as of Upper Devonic age. On the basis of the fish remains Dr Smith Woodward correlated these sandstones with the Lower Devonic Hereford beds. Further investigation will be required to fix their relation to the fish beds of Campbellton, N. B., and Migouasha, Quebec, which are now regarded as of later Devonic age.
- ↑ See Ami. Geolog. Soc. America Bul. 12: 301–12. 1901; Twenhofel. American Journal of Science, Aug. 1909; Williams, M. Y., Geol. Surv. Canada Rep't, 1911, p. 244.
- ↑ One of the "Pterygoti" described from Buffalo (P. globicaudatus) proves to be an Eurypterus, and a synonym of Hall's E. pustulosus.
- ↑ Although Grote and Pitt figured only the former, nearly the whole coxa is preserved in fainter outline [plate 79, fig. 1].
- ↑ The form of this edge and the peculiar shape of the entire segment led Pohlman to the erection of a new species, P. quadraticaudatus, on the supposition that it represents a telson.
- ↑ Obtained at Litchfield and possibly belonging to P. macrophthalmus.
- ↑ See Appendix.
- ↑ Sarle's description of this reads:
The shaft is nearly parallel sided, 3 mm broad and 12.5 mm long and curves at the end into a stout, striated, nearly perpendicular mucro 3.5 mm long. Back of this mucro is a series of 10 erect, sub triangular, striated denticles, very slightly separated at their bases. They are of three sizes, the largest or primaries being about one half the length of the mucro, the secondaries one half that of the primaries and the tertiaries about one half that of the secondaries. The first primary is separated from the mucro by a secondary and from the second primary by two secondaries and two tertiaries alternating; following the second primary are two secondaries separated by a tertiary. - ↑ Described as follows: An ovate metastoma 27 mm long and 16 mm wide, broadest just anterior to the middle, with the anterior corners slightly truncated, the lobes small and the terminal notch very narrow and shallow. It is marked by coarse, rounded, lobelike scales and is very much more robust than would be expected in Pterygotus monroensis. Judging by the ornamentation, it should be associated with the coarsescaled fragments most frequently found.
- ↑ Disjecta membra from the Frankfort shale, not referable to any genus.
Besides the few parts of the integument referred in the preceding descriptions to genera known from the Upper Siluric and Devonic, a considerable number of fragments have been found which cannot be placed with any degree of certainty with any of the genera; some are of noncommittal character, while others differ so strikingly from all later forms that they undoubtedly represent new types of greater than specific rank and must await future discoveries of more complete material, for description. We merely figure these here to indicate the richness of this new eurypterid fauna.
Plate 86, figure 18, is a coxa, possibly belonging to Pterygotus; plate 84, figure 17, the greater part of a broad, rapidly contracting abdomen, possibly belonging to Eusarcus, and plate 84, figure 19, a long, extremely slender, distinctly striated spine, suggesting Dolichopterus and Stylonurus.
Most indicative of the great diversity of forms occurring in the Frankfort beds are the well preserved patches of integument found in the black shale. Some of these have been mentioned in connection with the genera Eurypterus and Pterygotus. We figure here several patches bearing the ornamentation described of Eusarcus, Echinognathus and Megalograptus and exhibiting some variations [pl. 84, fig. 13–16]. Another style of ornamentation is represented by figure 8 of plate 83. This consists of extremely fine, very closely and evenly arranged tubercles. The patch of integument, reproduced in plate 85, figure 8, shows a mass of densely set, short, sharp spines and that shown in plate 85, figure 7, a profusion of long slender spines. Plate 85, figure 10, is a part of a supposed leg segment with a strange pattern of parallel raised lines connected by another set of shorter parallel oblique lines.