1911 Encyclopædia Britannica/Teleostomes

TELEOSTOMES, members of the third sub-class of the class Fishes, being all the fishes in which the skull is invested with membrane bones, viz., the Crossopterygians, the Dipnoans, the Ganoids and the Teleosteans. They may be further defined as fishes with an ossified or cartilaginous skeleton, a lower jaw, gills inserted on the gill-arches, a single gill-opening on each side (exceptionally fused with its fellow on the ventral side), an opercle formed of one or several bones, the body usually covered with scales or bony plates, an air-bladder or lung, at least in the primitive forms, and without copulatory paired organs or “ claspers.”

The term which designates this sub-class has been adopted by Sir R. Owen, E. D. Cope, and A. S. Woodward in a less comprehensive sense, the Dipneusti being regarded by them as constituting a separate slfb-class, and its inventor, C. L. Bonaparte (1838) had proposed it in a more restricted sense, the sturgeons, lophobranchs and plectognaths being excluded. T. Gill (1872) was the first to use it in the acceptation taken in the present article. Whether the Ostracophores should be included among the Teleostomes, as recently proposed by C. T. Regan, is still open to doubt. The sub-class is here divided into four orders, but it is difficult to decide whether, in an ascending series, the Crossopterygians or the Ganoids should be placed first. From the point of view of the evolution of the paired fins, accepting the lateral fin-fold theory as the better supported by the evidence at hand, there -is much to say in favour of regarding the Chondrostean Ganoids as the more primitive type. From another point of view the condition of the air-bladder in the existing Crossopterygians appears to represent the earliest form assumed by this important organ, which it seems rational to conclude was originally evolved as an accessory breathing organ and later became transformed into a hydrostatic apparatus (Ganoids and T eleosteans) on the one hand, into a true lung (Dipnoans and Batrachians) on the other. Guided by the second consideration, assuming that the air-bladder of the fossil Crossopterygians conformed to the type known in their recent representatives, and also in deference to palaeontological chronology, whatever it be worth in the present state of our knowledge, we shall begin the series with the Crossopterygians, which pass into the Dipnoans, and then take up the Ganoids, which lead up very gradually to the Teleosteans, the dominant group at the present day. But we do not deny the force of the arguments adduced by Regan in attempting to show that the paired fins of the Chondrostean Ganoids are a nearer approach to the primitive condition than are those of the Crossopterygians. No doubt some day we shall become acquainted with still older Teleostomes, which we may expect to establish the connexion between the two types which in Palaeozoic times have evolved on parallel lines. ORDER I.-C ROSSOPTERYGII

Paired fins, at least the pectorals, lobate, having an endo-skeletal axis more or less fringed with dermal rays. Mandibular arch suspended from the upper segment of the hyoid arch (hyostylic skull). Splenial bone present. No supra occipital bone. A pair of large jugular plates, sometimes with small lateral plates and an anterior azygous element, developed in the branchiostegal membrane between the mandibular rami. Heart with a'contractile, multivalvular conus arteriosus; intestine with a spiral valve; air bladder with pneumatic duct communicating with the ventral side of the oesophagus.

Maxillary bone large, toothed, bordering the mouth. Bones of the upper surface of the skull mostly paired. Pectoral arch with both clavicle (so-called infra-clavicle) and c lei thrum. Ventral fins inserted far back. With few exceptions (tail of Coelacanthidae, dorsal and caudal fins of Polypteridae) the dermal rays of the unpaired fins more numerous than their endo-skeletal supports, a primitive character also found in the lower Ganoids, but disappearing in the higher.

SUB-ORDER I.-OSTEOLEPIDA

(lncludin the Haplistia, Rhipidistia and Actinistia.) Pectoral fins obtuse?y or acutely lobate, articulating with the pectoral girdle by a single basal endo-skeletal element. Nostrils on the ower side of the snout. Two dorsal fins.

Families: Osteolepidae, Rhizodontidae, Holoptychidae, Coelacanthidae. The scales may be rhombic and thickly coated with ganoine (Osteolepidae) or cycloid. The vertebral axis is strongly hetero cereal in the Osteolepidae and Holoptychidae, and diphycercal or intermediate between the heterocercal and the diphycercal types in the other families; usually acentrous, sometimes with ring-like calcification's (some of the Rhizodontidae). In the Holoptychidae the pectoral fin is extremely similar to that of the Dipneusti of the family Dipteridae, which they resemble closely in form and scaling. Their teeth are remarkable for their complicated structure, resembling that of the Labyrinthodont Batrachians. A pineal foramen is present between the frontal bones in most of the Rhizodontidae. The Osteolepidae were mostly moderate-sized fishes, the largest (Megalichthys) measuring about 4 ft. in length. These Crossopterygians first appear in the Lower Devonian, are abundant in the Upper Devonian, Carboniferous and Permian; in later periods they are represented only by the more specialized Coelacanthidae, which appear in the Lower Carboniferous, and persist as late as the Upper Chalk.

C SUB-ORDER II.-CLADISTIA

Pectoral fin obtusel lobate, with three basal endo-skeletal elements. Nostrils on the upper side of the snout. A single dorsal fm, formed of a series of detached rays.

A single family: Polypteridae.

The existing Crossopterygians which form this sub-order differ very considerably from the extinct Osteolepida, perhaps quite as much as these differ from the Dipneusti. The ventral fins are not lobate, the vertebral column is well ossified and its termination is of the diphycercal type. Spiracles, covered by bony valves, are present on the upper surface of the head. The dorsal fin is unique among fishes, being formed of detached rays consisting of a spine like fulcral scale supporting the fringes of the ray; these rays have been regarded, erroneously, as representing so many distinct fins, or “ finlets." The scales are bony, rhombic and thickly coated with ganoine.

The Polypteridae are confined to tropical Africa and the Nile, and represented by two genera: Polypterur and Calamichthys, the former moderately elongate and provided with ventral fins, the latter serpentiform and devoid of ventrals. We now know ten species of Palypterus, from the Nile, the Congo, the rivers of West Africa, and lakes Chad, Rudolf and Tanganyika, and one 'of Calamichthys, which inhabits West Africa from the Niger delta to the Chiloango. The largest species of Polypterus reach a length of nearly 4 ft. The young are provided with an external opercular gill very similar to the gills of larval salamanders. The air-bladder acts as an accessory breathing organ, although these fishes are not known ever to leave the water. The development is stated by the late J. S. Budgett to be even more Batrachian-like than that of the Dipneusti, but the results of the study of the material collected by him shortly before his death have not yet been published.

Order II.—DIPNEUSTI

Often called Dipnoi, a term proposed for this order by Müller in 1845, but which had already been used for the Batrachians (F. Leuckart, 1821) before the discovery of Lepidosiren. The substitute Dipneusti (E. Haeckel, 1866) is, therefore, preferable. Paired fins lobate, or reduced to a jointed endo-skeletal axis. Upper segment of the mandibular arch confluent with the skull (autostylic skull). Praemaxillary and maxillary bones absent, dentary absent or small and toothless; teeth on the palato-ptegoid and splenial bones, sometimes also on the vomers. No supra occipital bone. Heart trilocular, with a contractile, multivalvular conus arteriosus; intestine with a spiral valve; air-bladder transformed into a single or double lung, opening at the glottis on the ventral side of the pharynx.

The cranial roof-bones include median as well as paired pilates, which cannot easily be homologized with those of other eleostomes; in the older forms, these bones are small and numerous, and, coated with ganoine, appear on the surface of the head, whilst in the later forms they are reduced in number as well as in the degree of ossification, and have sunk below the skin. Pectoral arch with both clavicle and c lei thrum. Ventral fins inserted far back. Vertebrae acentrous. Dermal rays of vertical fins much more numerous than their supports, which correspond in number to the neural and haemal arches. Nostrils on the lower side of the snout, the posterior within the mouth. Scales cycloid, (almost quadrate in Sagenodus, a genus of Ctenodontidae). Families: Dipteridae, Ctenodontidae, Uronemidae, Ceratodontidae, Lepidosirenidae.

The Dipteridae are heterocercal and have two dorsal fins, as in the Crossopterygian Holoptychidae; in the other families the dorsal fin is elongate and single, and extends to the extremit of the tail, which belongs to the diphycercal type. In the three fiist families, which are entirely Palaeozoic, ranging from the Devonian to the Permian, the dental plates nearly always exhibit more or less clearly the points of the separate denticles of which, as shown by the development of Neoreratodus, they were originally composed, but vomerine teeth, such as exist in the Ceratodontidae and Lepidosirenidae, do not appear to have existed. In the Dipteridae alone the scales were covered with dense, punctate ganoine, which has become much reduced or disappeared entirely in the other members of this order. The two first families had well-developed gular plates.

In the Ceratodontidae, which first appeared in the Trias and have persisted to the present day, the skull is more feebly ossified than in the earlier forms, and this may well be looked upon as a degeneration, since the head of the Triassic Ceratodus sluri, whilst exhibiting the same arrangement of bones as in the living form, differs in its higher degree of ossification; and as the dermal rays of the caudal fin also exhibit distinctive features in a fossil of the same period, it is advisable to refer the existing Ceralodus forsleri to a distinct genus, which has been named Neoceratodus by Castelnau (1876) and Epiceratodus by Teller (1891). But there can be no question that Neoceratodus is very closely related to Ccratodus. lts only known species, N. forsteri, variously known as the barramunda, flat-head, and Dawson or Burnett salmon, inhabits the Burnett, Dawson and Mary rivers in Queensland, and was first discovered in 1870. lts anatomy was made known by the memoir of A. Gunther, and numerous contributions by T. H. Huxley, E. R. Lankester, J. E. V. Boas, W. B. Spencer and others, whilst its development has been elaborately worked out by R. Semon. This fish, which grows to a length of 6 ft., has the body moderately elongate and compressed, covered with large thin scales, and the paired fins are acutely lobate, consisting of a median jointed axis fringed on each side by a series of radialia supporting nne dermal rays (archipterygium of C. Gegenbaur). Although provided with a lung, which is single, Neoceratodus never leaves the water. It feeds on both animal and vegetable matter, the specimens kept in the London Zoological Gardens readily eating lettuce in addition to frogs and bits of raw meat. The early development resembles very closely that of Batrachians, but there are no metamorphoses properly speaking, and at no period does the young possess external gills ora holder or cement or an. The South American Lepidosiren and the tropical African Protoptefus, which constitute together the family Lepidosirenidae, were discovered long before Neoceralodus, the former in 1836, the latter in 1839. These fishes are much more specialized than are the Ceratodontidae; the body is more or less eel-shaped, the scales are thinner, the paired fins are reduced to slender styliform appendages formed of a jointed axis with or without a unilateral fringe of cartilaginous rays bearing fine dermal rays, and-the lung is paired. The development is even more Batrachian-like than that of Neoceratodus, and the larvae are provided with a cement organ and four (Lepidosiren) or five (Protoplerus) fringed external gills, traces of which may persist throughout life in Protopterus. The habits and development of Lemdosiren have been investigated by J. Graham Kerr, and those of Protopterus by J. S. Budgett. In oth the eggs are deposited in nests in the water and the male keeps guard over the eggs and young. The food is both animal and vegetable, as in Neoceratodus. During the dry season, Protopteru; burrows in the mud of drying marshes and, surrounded by a cocoon formed of hardened mucus secreted by glands of the skin, it s nds weeks or months in a dormant condition, breathing exclusively; by its lungs; dry clay balls containing such cocoons have often been brought over to Europe, and when soaked in water, the Protopterus is released in a most lively condition. Three species of Protopterus are known from different parts of Africa, the type species being P. annectens, an inhabitant of West Africa, from the Senegal to the Niger, and Lake Chad. Of Lepfidosiren only one species is known, L. paradoxa, living in the Amazon and Paraguay basins.

Great uncertainty, and much difference of opinion among palaeichthyologists, still revail as to the position in the system of a group of Devonian fiishes, of which Coccosteus and Dinickthys are the best-known representatives. Long placed with the Ostracophores is a group instituted by Sir F. McCoy in 1848 under the name of Placodermi; they were removed from their vicinity by A. S. Woodward in 1889, and referred to the Dipnoans as an order which he proposed to call Arthrodira. This view was based mainly on the assumption that the skull was autostylic and that maxillary bones were not develo ed, and also on the resemblance, previously noticed by J. S. Newberry, between the dentition of Dinichthys and that of Propterus. Woodward's proposal has not met with general acceptance, but it is strongly supported by the recent investigations of C. R. Eastman, who has added fresh arguments in favour of the autostylic condition of the skull and the homology of the cranial roof-plates with those of the Dipnoans, the Ceratodontidae in particular. On the other side, B. Dean and L. Hussakof deny such homologies, and even regard the dental mechanism of the Arthrodira as something quite different from the jaws and teeth of other vertebrates, and revert to the view of McCoy in lacing the Arthrodira in a group Placodermata, which they regardg as a class co-ordinate in rank with such divisions as Cyclostomi and Pisces.

In the present state of our knowledge it is perhaps best to leave the Arthrodira with or near the Dipneusti. They are thus defined by Woodward: Fishes with both head and trunk armoured, in the more specialized genera the shield of' the abdominal re ion articulating with the head-shield in ginglymoid facettes %Gr. γίγγλυμος, a hinge) which admit of free motion (hence the name Arthrodira, joint-neck). No trace of a hyomandibular bone. jaws paralleled by those of the existing Dipneusti. Notochord persistent. Pectoral fins unknown; ventral fins rudimentary. Two families: Coccosteidae and Dinichthyidae, from the Devonian of Europe and North America.

Some of the species of Dinichythys reached a great size, the head sometimes measuring a metre across.

Order III.—GANOIDEI

Paired fins not lobate. Mandibular arch suspended from the upper segment of the hyoid arch (hyostylic skull). Splenial bone present. No supra occipital bone. Unpaxred fins often with fulcra Heart with a contractile, multivalvular conus arteriosus; intestine, with a spiral valve; air-bladder with pneumatic duct communicating with the dorsal side of the oesophagus.

Sub-order I.—CHONDROSTEI

Pectoral arch with both clavicle and c lei thrum. Ventral fin; inserted far back, with well-developed endo-skeletal rays (baseosts); dermal rays of the dorsal and anal fins more numerous than their endo-skeletal supports. Heterocercal. Vertebrae acentrous.

Families: Palaeoniscidae, Platysomidae Catopteridae, Belonorhynchidae, Chondrosteidae, Polyodontidae, Acipenseridae.

In the three first families (evonian to Jura), the mouth is and the maxillaries are the head are paired, body is covered with In the fourth family toothed, praemaxillary bones are present, large, the bones of the upper surface of branchiostegal rays are present, and the rhomboidal, typically ganoid bony scales. (Trias to Lias), the snout is much elongate, and longitudinal series of scutes extend along the body, one on the back, one on the belly, and one on each side. The Liassic Chondrosteidae show an approach to the stur ons, and form a sort of connecting link between them and the Palaieoniscidae. The mouth was edentulous, praemaxillary bones were absent, but the maxillary bone was well developed, though small; the membrane bones of the skull were paired; branchiostegal rays were present; scales were absent, except on the caudal lobe.

In the modern Polyodontidae and Acipenseridae, whose first representatives appear in the Eocene, praemaxillaries are absent and the mouth is edentulous (Acipenseridae) or beset with minute teeth (Polyodontidae), the membrane bones of the skull are more irregular and comprise azygous elements, branchiostegal rays are absent, and the body is naked or covered with small ossification's and longitudinal series of bony scutes, whilst the caudal fin is scaled exactly as in the Palaeoniscidae. Barbels are absent in the Polyodontidae.

In the Polyodontidae, represented by one species, the paddle fish or spoon-bill (Polyodon folium), in the Mississippi, Ohio and Missouri rivers of North America, and by another (Psephurus gladius) in the Yang-tse-kiang and Hoang Ho rivers of China, the snout is produced into a very long, spatulate (Polydon) or sub-conical (Psephurus) appendage, apparently useful in stirring up the mud of the thick waters in which these fishes live, and perhaps a tactile organ compensating the very reduced size of the eyes. Psephurus gladius is said to grow to a length of 20 ft. The sturgeons (Acipenseridae) are divided into two genera: Acipenser, distributed over the coasts and fresh waters of the temperate parts of the northern hemisphere, and Scaphirhynchus, inhabiting North America and Central Asia. About twenty species of Acipenser and five of Scaphirhynchus are known. The sturgeons are of great value for their flesh, their eggs (caviare) and the isinglass from the air-bladder; several species are migratory, ascending rivers to spawn. The largest species attain a length of 10 to 18 ft.

Sub-order II.—HOLOSTEI

Clavicle proper absent. Ventral fins inserted more or less far back, without or with mere rudiments of endo-skeletal rays; dermal rays of the dorsal and anal fins corresponding to their endoskeletal supports. Caudal fin of an abbreviate-heterocercal or homocercal type.

Families: Semionotidae, Macrosemiidae, Pycnodontidae, Eugnathidae, Pachycormidae, Lepidosteidae, Aspidorhynehidae, Amiidae.

First appear in the Permian with the Semionotidae, become abundant in the Trias, dominant in the Jurassic, begin to decline in the Cretaceous, and from the Eocene to the present day are reduced to the two families Lepidosteidae and Amiidae, the modern representatives of which inhabit the fresh waters of North America.

In most of the Holostei the scales are bony, rhombic and covered with an enamel-like (ganoine) coating, but there is every gradation between this so-called ganoid t pe of scaling and the cycloid ty e exemplified by the Amiidae. Fulcra also disappear in some of the more specialized types. The mouth is always large and toothed, and branchiostegal rays are invariably present; a sin le gular plate is often present. In the earlier groups the notochord was persistent, with or without annular centra, or with each centrum composed of two elements-pl euro cent rum and hypo cent rum; these elements remain distinct and alternate in the caudal region of the Amiidae, whilst in the Lepidosteidae the centra are as fully developed as in most Teleosteans, and opisthocoelous or convexo-concave.

The pike-like genus Lepidosteus was abundant in Europe in Eocene and Miocene times, and is now represented by three species in eastern North America, Mexico and Cuba. The largest species reaches a length of 10 ft. Amia, the bowfin, of similar geological age, is a much smaller fish. not exceeding 2 ft., from the eastern parts of North America. Its air-bladder is cellular and acts as an accessory breathing organ. It deposits its eggs in a sort of nest, which is protected by the male, who for some time accompanies the swarm of young fry and defends them with great courage.

Leedsia problematica, one of the Pachycormidae from the Oxford clay, probably reached a length of 30 ft., and is the largest known Teleostome.

Order IV.—TELEOSTEI

Paired fins non-lobate, the ventrals without baseosts. Mandible suspended from the upper segment of the hyoid arch. Splenial bone absent. Supraoccipital bone present. Heart without muscular conus arteriosus. or with much reduced conus, with one, exceptionally two, rows of valves. Air-bladder, if presen-t, communicating With the dorsal side of the oesophagus or digestive tract, or completely closed.

Sub-order I.—MALACOPTERYGII

Air bladder, if, present, with a duct. Opercle well developed. Pectoral arch suspended from the skull; mesocoracoid bone present. Fine without spines, the ventrals abdominal (rarely absent). Anterior vertebrae distinct, without Weberian ossicles., Families: Pholidophoridae, Archaeomenidae, Oligopleuridae, Leptolepidae, Elopidae, Albulidae, Mormyridae, Hyodontidae, Notopteridae, Osteoglossidae, Pantodontidae, Ctenothrissidae, Phractolaemidae, Saurodontidae, Chirocentridae, Clupeidae. Chanidae, Salmonidae, Alepocephalidae, Stomiatidae, Gonorhynchidae, Cromeriidae.

Unquestionably the most generalized sub-order, having most in common with the Holostean ganoids. The first four families, of Triassic to Cretaceous age, are so closely connected with these Ganoids that their allocation to the Teleosteans must be regarded as provisional. Some of the Pholidophoridae were flying fishes. The Elopidae and Albulidae are also low forms, traced back to the Cretaceous seas, having points in common with the Ganoids (gular plate in the former, conus arteriosus with two rows of valves in the latter). The Mormyridae are among the most extraordinary fishes, and, like the four families which follow in the above list, confined to fresh waters. Other families, like the Chirocentridae, Clupeidae and Salmonidae, are entirely or partly marine, the two last being of great economic importance. The Alepocephalidae and Stomiatidae are restricted to the deep sea.

See Anchovy, Herring, Menhaden, Mormyr, Pilchard, Salmonidae, Shad and Sprat.

Sub-Order II.-OSTARIOPHYSI

Air-bladder, if well developed, with a duct. Pectoral arch suspended from the skull; mesocoracoid bone present. Fins without spines, or dorsal and pectoral with a single spine formed by the co-ossification of the segments of an articulated ray. The anterior four vertebrae strongly modified, often co-ossified, and bearing a chain of small bones (so-called Weberian ossicles) connecting the air-bladder with the ear.

Families: Characinidae, Gymnotidae, Cyprinidae, Siluridae, Loricariidae, Aspredinidae.

One of the most natural groups of the class Pisces, as demonstrated by M. Sagemehl in 1885. The Characinidae are the most generalized, although perhaps not directly derived from the Amiid Ganoids, as believed by Sagemehl; they show great variety of form and dentition, and are confined to Central and South America and Africa. The Gymnotidae, which include the so-called electric eel, are closely related to the Characinidae, and occur only in South America. The largest families are the Cyprinidae and Siluridae. With the exception of a few Siluridae, the Ostariophysi are all fresh-water fishes.

Sub-Order III.—SYMBRANCHII

Eel-shaped fishes without paired fins, with the pectoral arch free or suspended from the skull, without mesocoracoid bone, and with the anterior vertebrae distinct, without-Weberian ossicles. Gill-openings confluent into a single, ventral slit. Air-bladder absent.

Families: Symbranchidae and Amphipnoidae.

Like the Apodes, which they resemble in general appearance, these fishes are no doubt derived from some low type with abdominal ventral fins, but whether from the Malacopterygii or the Haplomi we have as yet no data from which to conclude. Inhabitants of the fresh or brackish waters of south-eastern Asia, tropical America, Australia and Tasmania.

In the cuchia, Amphipnous cuchia, the gills are much reduced, and a respiratory air-sac extends on each side of the body behind the head, communicating with the gill-cavity.

Sub-Order IV.—APODES

Air-bladder, if present, with a duct. Praemaxillary bones absent; the maxillaries, if present, separated on the median line in front by the coalescent ethmoid and vomer. Pectoral arch, if present, not connected with and remote from the skull; mesocoracoid bone absent. Fins without spines, the ventrals absent. Anterior vertebrae distinct, without Weberian ossicles. Elongate, serpentiform fishes with naked skin, or with minute scales imbedded in the skin.

Families: Anguillidae, Nemichthyidae, Synaphobranchidae, Saccopharyngidae, Muraenidae.

A large group of aberrant, degraded fishes, heralded by the Cretaceous genus Urenchelys, the most generalized of eels. Mostly marine, many bathybial; some living principally in fresh water, but breeding in the sea, like the common eel (see articles Eel and Muraena).

Sub-Order V.—HAPLOMI

Air-bladder, if present, with a duct. Opercle well developed. Pectoral arch suspended from the skull; no mesocoracoid bone. Fins usually without, rarely with a few spines; ventrals abdominal, if present. Anterior vertebrae distinct, without Weberian ossicles. Families: Galaxiidae, Haplochitonidae, Enchodontidae, Esocidae, Dalliidae, Scopelidae, Alepidosauridae, Cetomimidae, Chirothricidae, Kneriidae, Cyprinodontidae, Amblyopsidae, Stephanoberycidae, Percopsidae.

The absence of the mesocoracoid bone distinguishes these fishes from the Malacopterygii, and the presence of a duct to the air bladder separates them from the Percesoces, to some of which, the Scombresocidae and the Atherinidae, they are linked by the Cyprinodontidae; whilst the Scopelidae are connected with the Berycidae by the Stephanoberycidae.

The type family of this sub-order is that of the Esocidae or pike, inhabitants of the fresh waters of Europe. northern Asia, and North America. The Galaxiidae are mostly fresh-water fishes and have a wide distribution in the southern hemisphere (southern parts of South America, New Zealand, South Australia and Tasmania, Cape of Good Hope), one species being identical in South America, the Falkland Islands, New Zealand and Tasmania. Their distribution has been regarded as affording support to the theory of an Antarctic continent in Tertiary times. However, several of the species spend part of their life, and even breed, in the sea, whilst others may be regarded as having become more recently adapted to fresh water, so that the argument derived from their range is not so strong as if we had to deal with exclusively freshwater fishes. The Cyprinodontidae are partly brackish, partly fresh-water fishes, whilst the Scopelidae, which are traced back to the Chalk, are all marine, many being inhabitants of great depths.

Sub-Order VI.—HETEROMI

Air-bladder without duct. Opercle well developed, parietal bones separating the frontals from the supra occipital. Pectoral arch suspended from the supra occipital or the epiotic, the post-temporal small and simple or replaced by a ligament; no mesocoracoid bone. Ventral fins abdominal, if present.

Families: Dercetidae, Halosauridae, Lipogenyidae, Notacanthidae, Fierasferidae.

Closely related to the Haplomi, but separated chiefly on account of the closed air-bladder. Mostly deep-sea fishes, some of which appeared as early as the Cretaceous period. The genus Fierasfer com rises small degraded fishes commensals of Holothurians and bivaive molluscs.

Sub-Order VII.—SELENICHTHYES

Air-bladder without duct. Opercle well developed. Pectoral arch suspended from the skull; no mesocoracoid bone. Fins without spines. Ventral fins abdominal, with very numerous (15 to 17) rays.

A very aberrant type, of uncertain affinities. Its only representative is the opah, Lampris luna, a large pelagic fish of wide distribution.

Sub-Order VIII.—THORACOSTEI

Embracing the Hemibranchii and Lophobranchii, but excluding the Hypostomides (Pegasidae), which the investigations of F. E. Jungersen show to be aberrant mail-cheeked Acanthopterygians.

Air-bladder without duct. Pectoral arch suspended rom the skull: no mesocoracoid bone. Ventral fins abdominal, if present. Branchial arches more or less reduced.

Families: Gastrosteidae, Aulorhynchidae, Protosyngnathidae, Aulostomatidae, Fistulariidae, Centriscidae, Amphisilidae, Solenostomidae, Syngnathidae. The two latter families institute the division Lophobranchii, in which the gill-lamellae are enlarged and orm rounded lobes.

See articles Sea-Horse, Stickleback, and Pipe-Fishes.

Sub-Order IX.—PERCESOCES

Air-bladder, if present, without duct. Parietal bones separated by the supra occipital. Pectoral arch suspended from the skull; no mesocoracoid bone. Ventral fins, if present, abdominal, or at least with the pelvic bones not solidly attached to the clavicular arch.

Families: Scombresocidae, Ammodytidae, Atherinidae, Mugilidae, Polynemidae, Chiasmodontidae, Sphyraenidae, Tetragonuridae, Stromateidae, Icosteidae, Ophiocephalidae, Anabantidae. This series of families connects the Haplomi with the Acanthopterygii. The Percesoces are mostly marine, but the two last families are exclusively fresh-water. Some are inhabitants of great depths, others are pelagic, like the flying-fish (Exocoetus).

Sub-Order X.—ANACANTHINI

Air-bladder without duct. Parietal bones separated by the supra occipital; prootic and ex occipital separated by the enlarged opisthotic. Pectoral arch suspended from the skull; no mesocoracoid bone. Ventral fins below or in front of the pectorals, the pelvic bones posterior to the clavicular symphysis and only loosely attached to it by ligament. Fins without spines. Families: Macruridae, Gadidae, Muraenolepididae. Nearly all marine. The Macruridae are among the most characteristic fishes of the great depths. The Gaclidae include some of the most valuable food-fishes.

Sub-Order XI.—ACANTHOPTERYGII

Air-bladder usually without duct. Opercle well developed; supra occipital in contact with the frontals. Pectoral arch suspended from the skull; no mesocoracoid bone. Ventral fins thoracic or jugular, more or less firmly attached to the clavicular Erch. Gill-opening usually large, in front of the base of the pectoral fin.

The character from which this sub-order, the most comprehensive of the whole class, derives its name, viz., the presence of non-articulated, spiny rays in the dorsal and anal fins, is by no means universal, exceptions to the rule being numerous.

Division I. Beryciformes.—Families: Berycidae, Monocentridae, Pol mixiidae.

The most primitive of the Acanthopterygians, already well represented in the Chalk. A duct has been observed to be sometimes present between the air-bladder and the digestive tract. All marine, several bathybial.

Division II. Perciformes.—Families: Pempheridae, Serranidae, Anomalopidae, Pseudochromididae, Cepolidae, Hoplognathidae, Sillaginidae, Sciaenidae, Scorpididae, Caproidae, Centrarchidae, Cyphosidae, Lobotidae, Toxotidae, Nandidae, Percidae, Acropomatidae, Gerridae, Lactariidae, Trichodontidae, Pristipomatidae, Sparidae, Mullidae, Latrididae, Haplodactylidae, Chaetodontidae, Drepanidae, Osphromenidae, Acanthuridae, Teuthididae, Embiotocidae, Cichlidae, Pomaoentridae, Labridae, Scaridae.

The Percidae, Centrarchidae, Toxotidae, Nandidae, Osphromenidae, Embiotocidae, and Cichlidae are fresh-water fishes, the others are all or nearly all marine. Aipichthys, which is included among the Scorpididae, is one of the few Acanthopterygian types known to have existed as early as the Cretaceous period.

See articles Cichlids, Mullet, Murray Cod, Parrot-Fishes, Perch, Pike-Perch, Sheepshead, Wrasse.

Division III. Scombriformes.—Families: Carangidae, Rhachicentridae, Scombridae, Trichiuridae, Histiophoridae, Xiphiidae, Luvaridae, Coryphaenidae, Bramidae.

Marine fishes, several being pelagic and among the largest Teleosteans and swiftest swimmers. See articles Hair-Tail, Mackerel, Pilot-Fish, Sword-Fish, Tunny.

Digision IV. Zeorhombi.—Families: Zeidae, Amphistiidae, Pleuronecti ae.

Division V., Kurtiformes.—A single family, Kurtidae, with a sin le genus and species from the Indian and Pacific oceans.

Division VI. Gobiiformesr- A single family, Gobiidae.

Division VII. Discocephali.—A single family, Echeneididae. The remarkable remoras attach themselves by means of a cephalic disk to boats or to sharks, turtles, cetaceans, and other large swift swimming animals. They form an isolated group, and have no real affingy with the Scombridae, with which they have long been associated.

Division VIII. Scleroparei.—Families: Scorpaenidae, Hexagrammidae, Comephoridae, Rhamphocottidae, Cottidae, Cyclopteridae, Platycephalidae, Hoplichthyidae, Agonidae, Pegasidae, Triglidae, Dactylopteridae.

The “Mail-cheeked” Acanthopterygians include a great variety of forms, mostly living in the sea, the best known being referred to iln the articles Flying-Fish, Gurnard, Lump-Sucker, and Miller’s Thumb.

Division IX. Jugulares.—Families: Trachinidae, Percophiidae, Leptoscopidae, Nototheniidae, Uranoscopidae, Trichodontidae, Callionymidae, Gobiesocidae, Blenniid e, Batrachidae, Pholididae, Zoarcidae, Congrogadidae, Ophidiidae, Podatelidae.

Nearly all marine, some deep-sea. Macrius amissus, which probably belongs to the Leptoscopidae, measures 5 ft. and is the largest known deep-sea Teleostean. The other members of this division are mostly small, Anarrhichas being another exception. The weevers (Trachinus) are dangerous stinging fishes.

Division X. Taeniosomi.—Families: Trachypteridae, Lophoti ae.

Deep-sea or pelagic fishes, some attaining a large size.

Sub-Order XII.—OPISTHOMI

Air-bladder without duct. Opercle well developed, hidden under the skin; supra occipital in contact with the frontals. Pectoral arch suspended from the vertebral column, far behind the skull; no mesocoracoid bone. Vertical fins with spines. Ventral fins absent. .

Eel-shaped fishes standing in the same relation to the Acanthopterygii as do the Apodes to the Malacopterygii. The single family, Mastacembelidae, is possibly derived from the Blenniidae. Fresh and brackish waters of southern Asia and tropical Africa.

Sub-Order XIII.—PEDICULATI

Air-bladder without duct. Opercle well developed, hidden under the skin; supra occipital in contact with the frontals. Pectoral arch suspended from the skull; no mesocoracoid bone. Ventral fins, if present, jugular. Gill-opening reduced to a foramen situated in or near the axil more or less posterior to the base of the pectoral fin. Body naked or covered with spines or bony tubercles.

Connected with the Acanthopterygii Jugulares through the Batrachidae.

Families: Lophiidae, Ceratiidae, Antennariidae, Gigantactinidae, Malthidae.

Curiously aberrant marine fishes, many bathybial. The best known are the fishing-frog or angler, Lophius, and the Antennarius, which lives in coral groves or is carried about in mid-ocean among

the Sargassum weeds.

Sub-order XIV.—PLECTOGNATHI

Air-bladder without duct. Opercular bones more or less reduced; supraoccipital in contact with the frontals; maxillary and praemaxillary bones often firmly united. Pectoral arch suspended from the skull. No ribs. Ventral fins thoracic and much reduced if present; the pelvic bones, if present, more or less co-ossified. Gill-opening much reduced. Body covered with more or less osseous scales, bony scutes, or spines, or naked.

A highly aberrant group, closely connected with the Acanthopterygii through the Acanthuridae.

Division I. Sclerodermi.—Families: Triacanthidae, Triodontidae, Balistidae, Ostraciontidae.

Division II. Gymnodontes.—Families: Tetrodontidae, Diodontidae, Molidae.

The Plectognaths are all marine; the recently discovered Triacanthid Halimochirurgus, remarkable for its long, tube-like snout, from the Gulf of Manaar, is the only form of this sub-order which is confined to the deep sea. Although so highly specialized, several forms, such as Ostracion (the coffer-fish), Tetrodon and Diodon, were already represented in the upper Eocene. See File-Fish, Globe-Fish and Sun-Fish.

For bibliographical references to the Teleostomi, see Ichthyology.

(G. A. B.)