Chapter XXIV: Appendix: To the Fishes: Palaeospondylidae—ostracodermi—heterostraci (5)

FAM. 3. PEMPHERIDAE.—The resemblance which the fishes united under this family bear to _Beryx_ is very striking, and applies to the skeleton as well as to the external characters. But the ventral fins are formed of one spine and five soft rays, as in most Acanthopterygians. _Bathyclupea_ agrees with _Beryx_ in {657}being possessed of an open duct to the air-bladder. About twelve species are known, referable to four genera: _Pempheris_, _Parapriacanthus_, _Neopempheris_, from the Indian, Pacific, and tropical Atlantic Oceans, and the deep-sea _Bathyclupea_, from the Indian and Caribbean Seas, at depths of 145 to 419 fathoms.

FAM. 4. CENTRARCHIDAE.—No subocular lamina of the suborbitals, or subocular shelf; entopterygoid present; palate toothed; teeth conical. Praecaudal vertebrae with transverse processes from the third or fourth to the last; ribs mostly sessile, behind the transverse processes. Two nostrils on each side. Gill-membranes free from isthmus; 5 to 7 branchiostegal rays; gills 4, a slit behind the fourth; pseudobranchiae more or less developed, often rudimentary or absent. Lower pharyngeal bones separate. Soft portion of dorsal fin not more developed than the anal. Carnivorous freshwater fishes, some entering brackish water. Many are known to build nests. Mostly inhabitants of North America, the best known being the Sun-Fishes (_Lepomis_), and Black Bass (_Micropterus_), several species of which have recently been introduced into continental Europe. Principal genera: _Pomoxys_, _Centrarchus_, _Ambloplites_, _Chaenobryttus_, _Micropterus_, _Lepomis_, _Elassoma_, _Kuhlia_. Thirty-two species are known.

FAM. 5. CYPHOSIDAE.—Herbivorous fishes, agreeing in their essential osteological characters with the preceding, differing in the incisor-like outer teeth and densely-scaled fins. Some 14 species are known, from the Pacific and Indian Oceans, referable to 4 genera: _Cyphosus_ (_Pimelepterus_), _Hermosilla_, _Sectator_, _Medialuna_.

{658}FAM. 6. LOBOTIDAE.—As in Centrarchidae, but transverse processes of vertebrae very short, and palate toothless. Two genera: _Lobotes_, with two species from the warm parts of the Indian and Pacific Oceans, the Mediterranean, and the Atlantic coast of America, and _Datnioides_, with two species from the estuaries of the Ganges and the rivers of Burma, Siam, and the Malay Peninsula and Archipelago.

FAM. 7. TOXOTIDAE.—No subocular shelf; entopterygoid present; palate toothed; mouth very protractile; maxillary very slender. Ribs sessile, behind parapophyses which commence from the third vertebra. Two nostrils on each side. Gill-membranes free from isthmus; 7 branchiostegal rays; gills 4, a slit behind the fourth; pseudobranchiae present. Lower pharyngeal bones separate. Ventral fins with 1 spine and 5 soft rays.

A single genus, _Toxotes_, with 5 species from the fresh waters and coasts of the East Indies, N. Australia, Polynesia, and New Zealand. _Toxotes jaculator_ derives its name from its habit of capturing insects flying near the surface of the water by shooting drops of water at them, a habit which it continues in captivity.

FAM. 8. NANDIDAE.—No subocular shelf; no entopterygoid; palate toothed; mouth very protractile. Praecaudal vertebrae with parapophyses from the 7th or 8th; ribs mostly sessile, behind the parapophyses. Two nostrils on each side. Gill-membranes free from isthmus; 6 branchiostegal rays; gills 4, a slit behind the fourth; pseudobranchiae absent. Lower pharyngeal bones separate. Soft portion of dorsal fin not more developed than the anal. Ventral fins with 1 spine and 5 soft rays.

Small carnivorous freshwater fishes, of which 14 species are known, referable to 6 genera: _Nandus_, _Catopra_, and _Badis_ from South-Eastern Asia, _Polycentropsis_ from West Africa, _Polycentrus_ and _Monocirrus_ from South America.

FAM. 9. PERCIDAE.—No subocular lamina of the suborbitals; entopterygoid present. Anterior vertebrae without transverse processes; all or most of the ribs inserted on the transverse processes when these are developed. Two nostrils on each side. Mouth not or but feebly protractile. Gill-membranes free from the isthmus; 6 to 8 branchiostegal rays; gills 4, a slit behind the fourth; pseudobranchiae more or less developed, often rudimentary, rarely absent. Lower pharyngeal bones separate. Soft portion of dorsal fin not very much more developed than {659}the anal; latter with 1 or 2 spines only. Ventrals with 1 spine and 5 soft rays.

Embrace about 90 species from the freshwaters of the Northern Hemisphere, referable to 12 genera: _Perca_, _Lucioperca_, _Percina_, _Etheostoma_, _Boleosoma_, _Ulocentra_, _Diplesium_, _Ammocrypta_, _Crystallaria_, _Aspro_, _Percarina_, _Acerina_. The British representatives of this family are the Perch (_Perca fluviatilis_) and the Pope (_Acerina cernua_). The largest forms are the Pike-Perches or Sander (_Lucioperca_) of Eastern Europe, Western Asia, and North America, which reach a length of 4 feet and are highly valued for the table. The American Darters (_Etheostoma_ and allies), on the other hand, are among the smallest fishes, but many are remarkable for their brilliant coloration.

FAM. 10. ACROPOMATIDAE.—An ill-defined group of marine fishes, some deep-sea, placed here provisionally as annectant between the Percidae and the Serranidae (Pomatominae), differing from the latter in the absence of a subocular shelf. Spinous dorsal short.

About 28 species, mostly from the Pacific Ocean, distributed in 9 genera: _Propoma_, _Xenichthys_, _Xenocys_, _Synagrops_, _Malacichthys_, _Acropoma_, _Melanostoma_, _Epigonus_ (_Telescops_), _Dinolestes_.

FAM. 11. SERRANIDAE.—Second suborbital with an internal lamina supporting the globe of the eye; entopterygoid present; palate usually toothed. Anterior vertebrae without transverse processes; all or most of the ribs inserted on the transverse processes where these are developed. Two nostrils on each side. Gill-membranes free from isthmus; 6 or 7 branchiostegal rays; gills 4, a slit behind the fourth; pseudobranchiae usually present. Lower pharyngeal bones usually separate. Soft portion of dorsal usually not much more developed than the anal. Ventral fins with 1 spine and 5 (rarely 4) soft rays.

One of the largest families of fishes. The principal genera may be grouped as follows:—

SERRANINAE.—_Percichthys, Percilia, Lateolabrax, Niphon, Morone, Percalates, Ctenolates, Macquaria, Siniperca, Coreoperca, Acanthistius, Trachypoma, Centrogenys, Polyprion, Oligorus, Stereolepis, Dinoperca, Liopropoma, Aulacocephalus, Plectropoma, Epinephelus, Cromileptes, Paranthias, Serranus, Centropristes, Chelidoperca, Gilbertia, Caesioperca, Caprodon, Anthias, Callanthias, Pseudoplesiops, Plesiops, Trachinops_.

{660}GRAMMISTINAE.—_Grammistes, Rhypticus_. PRIACANTHINAE.—_Priacanthus, Pseudopriacanthus_. CENTROPOMINAE.—_Lates, Psammoperca, Centropomus_. POMATOMINAE.—_Pomatomus, Scombrops_. AMBASSINAE.—_Ambassis_. CHILODIPTERINAE.—_Chilodipterus, Apogon_. LUTJANINAE.—_Lutjanus, Glaucosoma, Therapon, Hoplopagrus, Etelis, Aprion, Aphareus, Odontonectes_. CIRRHITINAE.—_Cirrhites, Cirrhitichthys_. PENTACEROTINAE.—_Pentaceros, Pentaceropsis, Histiopterus_.

The number of recent species amounts to about 550, the great majority of which are marine.

The earliest fossil form is _Prolates_, from the Upper Cretaceous of France. _Morone_, _Serranus_, _Percichthys_, _Anthias_, and _Apogon_ are represented in Eocene and later strata.

The range of the family is almost cosmopolitan; few of the Marine Perches descend to any great depth. Some of the species of _Stereolepis_ and _Epinephelus_ grow to a length of 6 to 10 feet. Several species of _Serranus_ (_S. cabrilla_, _S. scriba_, _S. hepatus_), inhabiting the Mediterranean and neighbouring parts of the Atlantic, and some _Lutjanus_ are normally hermaphrodite. Some _Chilodipterus_ and _Apogon_ are remarkable for their nursing habits, the male sheltering the eggs in his mouth.

The curious genera _Anomalops_ and _Photoblepharon_, of each of which a single species is known from the Malay Archipelago and the South Pacific, have been made the types of a family, ANOMALOPIDAE, the systematic position of which remains uncertain since the osteological characters have not been examined. {661}They are remarkable for the movable flap below the eye, bearing a luminous organ, the nature of which has recently been investigated by Max Weber.[714]

FAM. 12. PSEUDOCHROMIDIDAE.—Closely allied to the Serranidae, and connected with them through _Plesiops_ and its allies. Dorsal and anal fins elongate and formed mostly of articulated soft rays, the spines being feeble and few.

A. With two lateral lines: _Pseudochromis_, _Cichlops_.

B. With a single lateral line: _Opisthognathus_, _Latilus_, _Caulolatilus_, _Lopholatilus_, _Malacanthus_, _Bathymaster_, _Rathbunella_.

Marine, mostly of small size, inhabiting the Atlantic, Indian, and Pacific Oceans. About 30 species. One of the largest and best-known members of this family is the Tile-Fish (_Lopholatilus chamaeleonticeps_), living upon the bottom of what is known as the Gulf Stream slope, off the coast of New England, where it was first observed in 1879. Here the water is normally comparatively warm, coming as it does from the superheated region of the Gulf of Mexico. During a series of unusually severe gales in 1882, this mass of water was pushed aside, as it were, and replaced by colder water. As a result, millions and millions of these fishes were killed, and their dead bodies literally covered the surface of the sea for hundreds of square miles. It was feared that the Tile-Fish was exterminated; this was not so, however, and the fish has reappeared in tolerable abundance within the last few years.

FAM. 13. CEPOLIDAE.—Agree in essential characters with the preceding, but body band-like with very numerous vertebrae {662}(15 + 54), and very elongate dorsal and anal fins formed of soft rays, of which all except the first three dorsal and the first anal are articulated and branched.

Although these fishes have hitherto been placed near the Blenniidae, the Gobiidae, or the Trachypteridae, they are nothing but extremely elongate Perches, and they stand in the same relation to the Serranidae as the Trichiuridae to the Carangidae and Scombridae. They hardly deserve to rank as a family distinct from the Pseudochromididae.

Two genera, _Cepola_ and _Acanthocepola_, with 10 species, from the Mediterranean and North-Eastern Atlantic, the Indian Ocean, and the Western Pacific. The Band-Fish (_Cepola rubescens_), which is common in the Mediterranean, is sometimes found on the British coasts; it grows to a foot and a half in length, and is remarkable for its bright red colour.

FAM. 14. HOPLOGNATHIDAE.—Characters of Serranidae, but teeth fused to form a beak as in _Tetrodon_; palate toothless.

_Hoplognathus_, with 4 species, from the Pacific Ocean.

FAM. 15. SILLAGINIDAE.—As in Serranidae, but soft dorsal and anal much elongate, as in Pseudochromididae, from which the Sillaginidae differ in the separate spinous dorsal. Palate toothed. Connecting the Serranidae and the Sciaenidae.

Small Marine Fishes from the Indian and Pacific Oceans, ascending rivers. A single genus, _Sillago_, with about 10 species.

{663}FAM. 16. SCIAENIDAE.—Also closely related to the Serranidae. Dorsal fin with a short spinous and a long soft portion; anal much shorter than the latter. Palate usually toothless.

A large family of about 150 species, mostly marine. Principal genera: _Arripis, Sciaena, Corvina, Otolithus, Ancylodon, Nebris, Larimus, Pogonias, Haplonotus, Umbrina, Eques_.

Many of these fishes reach a large size, and the flesh of nearly all is esteemed. The Meagre (_Sciaena aquila_) is sometimes taken on our coast. The Drum (_Pogonias chromis_) so called from the sounds which it produces, in common with many other Sciaenids, is remarkable for having the lower pharyngeal bones united, as is also the case in the North American freshwater genus _Haplonotus_. The air-bladder is usually large and complicated, provided with more or less numerous appendages.

FAM. 17. GERRIDAE.—Agree in the character of the vertebral column with the Serranidae, but differ in the absence of a subocular shelf; the very protractile mouth usually descends when protruded and the praemaxillary emits an upward lateral process; palate toothless; lower pharyngeal bones usually large and more or less completely coalesced.

About 60 species of carnivorous, mostly small, fishes, from the tropical seas, referable to 3 genera: _Gerres, Equula, Gazza_.

FAM. 18. LACTARIIDAE.—Intermediate between Serranidae and Trichodontidae. No subocular shelf; palate toothed; branchiostegal rays 7; scales small, cycloid, deciduous; spinous dorsal short; anal longer than the soft dorsal; scapula with two foramina.

_Lactarius delicatulus_, from the coasts of Southern Asia.

FAM. 19. TRICHODONTIDAE.—Agree in the character of the vertebral column with the Serranidae, but have no subocular shelf; body naked, and anal much longer than the soft dorsal; palate toothless; only 5 branchiostegal rays.

Two genera, each with a single species, from the North Pacific, _Trichodon_ and _Arctoscopus_, bearing some resemblance to the Trachinidae, with which they have usually been associated.

FAM. 20. LATRIDIDAE.—Marine Fishes intermediate between the Serranidae and the Haplodactylidae, agreeing with the former in the extent of the anal fin, which is nearly as long as the soft dorsal, and with the latter in the absence of a subocular shelf and the posterior position of the ventrals. A single genus, _Latris_, with 3 or 4 species, from the coasts of Australia and New Zealand.

{664}FAM. 21. HAPLODACTYLIDAE.—No subocular shelf; entopterygoid present; palate usually toothless. Vertebrae with transverse processes from the third or fourth; all the ribs attached to the transverse processes when these are present; anterior epipleurals strong. Two nostrils on each side. Gill-membranes free from the isthmus; 5 or 6 branchiostegal rays; gills 4, a slit behind the fourth; pseudobranchiae present. Lower pharyngeal bones separate. Soft portion of the dorsal fin much more developed than the anal. Ventral fins with 1 spine and 5 soft rays, inserted far back behind the pectorals, the lower rays of which are simple and more or less thickened.

This family embraces the genera _Haplodactylus, Chilodactylus, Chironemus_, and _Threpterius_, with some 30 species from the seas of the Southern Hemisphere and Japan. They feed chiefly on crustaceans, molluscs, and other invertebrates living among sea-weed.

FAM. 22. PRISTIPOMATIDAE.—No subocular shelf; entopterygoid present; palate toothless. Vertebrae with transverse processes from the third; all the ribs attached to the transverse processes. Two nostrils on each side. Gill-membranes free from isthmus; 5 to 7 branchiostegal rays; gills 4, a slit behind the fourth; pseudobranchiae present. Lower pharyngeal bones separate. Ventral fins with 1 spine and 5 soft rays.

_Pristipoma, Haemulon, Diagramma_, and _Pentapus_, distributed over all the tropical and subtropical seas, a few entering fresh waters. About 130 species are known.

FAM. 23. SPARIDAE.—Second suborbital with an internal lamina supporting the globe of the eye; entopterygoid present; palate usually toothless; teeth often either cutting in front, or molar-like on the sides. Vertebrae with transverse processes from the second or third; all the ribs attached to the transverse processes. Two nostrils on each side. Gill-membranes free from isthmus; 5 to 7 branchiostegal rays; gills 4, a slit behind the fourth; pseudobranchiae present. Lower pharyngeal bones separate. Soft portion of dorsal fin not much more developed than the anal. Ventral fins with 1 spine and 5 soft rays.

The Sea-Breams embrace some 200 species, distributed over the coasts of nearly the whole world. Some are herbivorous, but the majority are carnivorous.

Principal genera: _Scolopsis, Dentex, Synagris, Caesio, Maena, Oblata, Melambaphes, Girella, Doydixodon, Cantharus, Box_, {665}_Crenidens, Pachymetopon, Dipterodon, Sargus, Charax, Lethrinus, Sphaerodon, Sparus, Pagrus, Pagellus_.

Abundantly represented in Eocene and Miocene beds by remains of _Sargus, Sparus, Pagrus, Pagellus_, and by the extinct genera _Ctenodentex, Sparnodus_, and _Trigonodon_. Some species grow to a length of three feet, such as the "Sheep's-Head" of North America, one of the best salt-water fishes of the United States, and the "Schnapper" (_Sparus unicolor_), of Australia, also much esteemed. Some of the Atlantic and Mediterranean species of _Box, Sargus, Charax, Sparus_, and _Pagellus_ are known to be normally, or at least very frequently, hermaphrodite.

FAM. 24. MULLIDAE.—The "Red Mullets" are very nearly related to the Sparidae, with which they agree in the structure of the vertebral column and the presence of a subocular shelf. They differ in the very weak dentition, the presence of a pair of hyoid barbels, the reduced number (4) of branchiostegal rays, and the double perforation of the scapula. Two short dorsal fins, remote from each other, the anterior with weak spines.

Small marine and brackish-water fishes, feeding on animalcules and decomposing matter; inhabitants of nearly all the tropical seas and extending to Northern Europe. About 50 species are known, referred to 5 genera: _Upeneoides, Upeneichthys, Mullus, Mulloides_, and _Upeneus_.

{666}The British species are _Mullus barbatus_ and _M. surmuletus_, remarkable for their beautiful pink or red colour, and much valued on the market, although no longer held in the high estimation for which they were noted by the Romans.

FAM. 25. SCORPIDIDAE.—Second suborbital with an internal lamina supporting the globe of the eye; entopterygoid present; palate toothed. Ribs sessile, behind the parapophyses when these are present. Two nostrils on each side. Gill-membranes free from isthmus; 7 branchiostegal rays; gills 4, a slit behind the fourth; pseudobranchiae present. Lower pharyngeal bones separate. Ventral fins, if present, with 1 spine and 5 soft rays.

This family embraces 12 species from the coasts of Africa, Southern Asia, Australia, and New Zealand, referable to 5 genera: _Scorpis_, _Atypichthys_, _Atyposoma_, _Henoplosus_, _Psettus_. The fish here figured (_Psettus sebae_, Fig. 408) is remarkable for the excessive depth of the body, which is greater than in any other species.

_Aipichthys_, one of the few Acanthopterygian types known to have existed in the Cretaceous period, appears to belong to the family Scorpididae as here defined, and not to the Carangidae.

FAM. 26. CAPROIDAE.—Characters of Scorpididae, but supratemporal completely ankylosed to the skull.

The Boar-Fish (_Capros aper_) of the Atlantic and Mediterranean is occasionally found on our southern coasts, and is highly remarkable for the hair-like bristles with which its scales are {667}covered, an extreme exaggeration of the "Ctenoid" type. The mouth is very protractile, and the vertebrae are only 22 or 23 in number. _Antigonia_, with a single species found at remote points in the Atlantic, Pacific, and Indian Oceans, is probably allied to _Capros_, with which it is believed to be connected through the fossil genus _Proantigonia_, from the Upper Miocene of Croatia.

FAM. 27. CHAETODONTIDAE.—Closely allied to and evidently derived from the more generalised types of the Scorpididae, differing in the attachment of the gill-membranes to the isthmus. Post-temporal more or less firmly united with the skull, sometimes indistinctly bifurcate. Mouth small; palate toothless; soft portions of vertical fins usually covered with scales; ribs usually strong and blade-like; body short and deep.

A large group of about 200 marine carnivorous fishes from the tropics, mostly of small size, remarkable for their singular forms and markings and brilliant coloration. They are particularly abundant about volcanic rocks and coral reefs.

{668}An Atlantic species of _Ephippus_ (_E. faber_) is extremely remarkable, when adult, for an enormously enlarged globular bony mass on the back of the head, formed by hypertrophy of the frontal and supraoccipital bones.

Principal genera: _Ephippus, Parapsettus, Scatophagus, Chaetodon, Chelmo, Heniochus, Holacanthus, Pomacanthus, Platax_.

_Chaetodon, Holacanthus, Pomacanthus, Scatophagus, Ephippus_, and _Platax_ were represented in the Eocene of Europe.

FAM. 28. DREPANIDAE.—The genus _Drepane_, with a single species from the Indian Ocean, is very closely related to the Chaetodontidae, but it lacks the subocular shelf, and it is distinguished externally by the very elongate, falciform pectoral fin.

FAM. 29. ACANTHURIDAE.—A more or less developed subocular shelf; entopterygoid present. Mouth very small, not or but slightly protractile, the maxillary more or less firmly attached or ankylosed to the praemaxillary; teeth conical, bristle-like, or incisor-like. Palate toothless. Vertebrae 22 or 23, the praecaudals with strong transverse processes commencing from the first; ribs and epipleurals inserted on the transverse processes. Post-temporal not distinctly forked, ankylosed to the skull. Two nostrils on each side. Gill-membranes broadly attached to the isthmus; 4 or 5 branchiostegal rays; gills 4, a slit behind the fourth; pseudobranchiae present. Lower pharyngeal bones separate. Body covered with minute, often rough scales. Dorsal and anal fins elongate, with more or less strong spines. Ventrals with 1 spine and 2 to 5 soft rays.

A family of about 80 species, mostly herbivorous, from the tropical seas, referred to 6 genera: _Zanclus, Ctenochaetus, Acanthurus, Colocopus, Prionurus, Naseus_. They form a connecting link between the Chaetodontidae and the Plectognathi.

Remains from the Eocene of Europe have been referred to _Zanclus, Acanthurus_, and _Naseus_, and to the extinct genera _Aulorhamphus_ and _Apostasis_.

FAM. 30. TEUTHIDIDAE.—No subocular shelf; entopterygoid present. Mouth very small, beak-like, not protractile, with incisor-like teeth; maxillary ankylosed to the praemaxillary. Palate toothless. Two nostrils on each side. Gill-membranes broadly attached to the isthmus; 5 branchiostegal rays; gills 4, a slit behind the fourth; pseudobranchiae present. Lower pharyngeal bones separate. Supratemporal forked. Vertebrae {669}23, with sessile ribs and no parapophyses, the epipleurals inserted on the ribs. Body covered with very small scales. Vertical fins elongate, with strong spines, 6 or 7 in the anal. Ventrals with 2 spines and 3 soft rays between them.

A single recent genus, _Teuthis_, with about 30 species, herbivorous fishes from the Indian and Western Pacific Oceans. According to Bottard[715] the sting from the spines of these fishes is much dreaded. _Archaeoteuthis_, from the Oligocene of Switzerland.

FAM. 31. OSPHROMENIDAE.—Second suborbital with a more or less developed internal lamina; entopterygoid present; palate toothed. Most of the praecaudal vertebrae with transverse processes, to which the ribs are attached. Two nostrils on each side. Gill-membranes attached to isthmus; 4 to 6 branchiostegal rays; gills 4, a slit behind the fourth; pseudobranchiae absent. Lower pharyngeal bones separate. Vertical fins very variable in extent, the spines sometimes very numerous, sometimes absent. Ventral fins with not more than 5 soft rays, sometimes reduced to a filamentous ray. A superbranchial respiratory organ, situated in a cavity above the gills.

Freshwater fishes having much in common with the Anabantidae, and likewise confined to South-Eastern Asia and Africa. Only 22 species are known, referable to 7 genera: _Helostoma_, _Polyacanthus_, _Osphromenus_, _Trichogaster_, _Luciocephalus_, _Betta_, and _Micracanthus_. The latter, the only African representative of the family (one species from the Ogowe), hardly differs from the Malay genus _Betta_. Most of the Osphromenidae are notable as aquarium fishes. The largest species, the Gourami (_Osphromenus olfax_), growing to a length of 2 feet, from the Malay Archipelago, is one of the best flavoured fishes of the Far East and has been acclimatised in India, the Guianas, and Mauritius. A domesticated variety of the Chinese _Polyacanthus opercularis_, known as _Macropodus viridi-auratus_, remarkable for the beauty of its form and colour, readily breeds in our aquariums. Like the Gourami, the male constructs a nest of air-bubbles, strengthened by a buccal secretion, and watches over the eggs and young. The little _Betta pugnax_, from South-Eastern Asia, derives its name from its excitable nature, which causes specimens to be kept by the Siamese in glass vessels where they engage in fights, special breeds being cultivated for the purpose. According to Cantor, {670}the Siamese in 1840 were as infatuated with the combats of these fishes as the Malays are with their cock-fights, and the licence to exhibit them was farmed, bringing in a considerable annual revenue to the king.

FAM. 32. EMBIOTOCIDAE.—Second suborbital with an internal lamina supporting the globe of the eye; entopterygoid present; palate toothless. Ribs sessile, above and behind the parapophyses, where these are present. Two nostrils on each side. Gill-membranes free from isthmus; 5 or 6 branchiostegal rays; gills 4, a slit behind the fourth; pseudobranchiae present. Lower pharyngeals united, with conical or pavement-like teeth. Anal fin, with three spines. Ventral fins with 1 spine and 5 soft rays.

Small or moderate-sized fishes inhabiting California and Japan, mostly marine, one species, however, inhabiting fresh waters, whilst another descends to a great depth. They feed mostly on crustaceans, but one genus (_Abcona_) is herbivorous. The name "Surf-Fishes," by which they are generally known, refers to the fact that most species are found in the surf along sandy beaches. All are viviparous in the strictest sense of the term, the young remaining for a long time closely packed in a sac-like enlargement of the oviduct analogous to a uterus; they are of relatively large size at birth, and quite similar in form to the parent, whilst at an earlier period they differ in having the vertical fins much more elevated. Twenty-four species are known.[716] Principal genera: _Hysterocarpus_, _Abcona_, _Cymatogaster_, _Embiotoca_, _Ditrema_.

FAM. 33. CICHLIDAE.—No subocular shelf; entopterygoid {671}present; palate toothless; lower pharyngeal bones more or less completely united, with median suture. Vertebrae with parapophyses from the third; ribs most frequently sessile or subsessile. A single nostril on each side. Gill-membranes free from isthmus; 5 or 6 branchiostegal rays; gills 4, a slit behind the fourth; pseudobranchiae absent. Dorsal fin, with numerous spines; anal with 3 spines or more. Ventral fins with 1 spine and 5 soft rays.

Fresh or brackish-water fishes, variable in form and dentition, some carnivorous, others chiefly herbivorous. In some American forms (_Cichla_) the males and females differ during the spawning season, the male developing a hump on the top of the head, which disappears afterwards. The eggs and young are cared for by the parents; either the male or the female, according to the species, sheltering them in the mouth or pharynx.[717] These fishes, often designated as "Chromides," a name which properly pertains to members of the following family, inhabit Africa, Madagascar, Syria, India and Ceylon, and Central and South America, from Texas to Uruguay. About 45 genera are distinguished, based mostly on the number of anal spines and the dentition, which for variety of types is comparable to that of the Characinidae. Of these 45 genera, 30 are African. 150 species are known from Africa (with Syria and Madagascar), 140 from America, and 3 from India and Ceylon.[718] Principal genera—African: _Lamprologus_, _Hemichromis_, _Paratilapia_, _Xenotilapia_, _Tropheus_, _Tilapia_, {672}_Asprotilapia_, _Eretmodus_, _Plecodus_, _Pseudetroplus_. American: _Acara_, _Heros_, _Hygrogonus_, _Cichla_, _Crenicichla_, _Chaetobranchus_, _Geophagus_, _Symphysodon_, _Pterophyllum_. Indian: _Etroplus_.

No part of the world surpasses Lake Tanganyika in variety of generic and specific types of Cichlidae, the fish-fauna of this great lake being in great majority made up of members of this family.

_Priscacara_, from the Eocene of North America, is the only extinct genus which can be referred to this family.

FAM. 34. POMACENTRIDAE.—A subocular shelf; entopterygoid present; palate toothless; teeth conical or incisor-like; lower pharyngeals completely united into one bone. Vertebrae with transverse processes from the fourth or fifth; ribs inserted on the transverse processes, when these are present. A single nostril on each side. Gill-membranes free from the isthmus; 5 to 7 branchiostegal rays; gills 3½; pseudobranchiae present. Dorsal fin elongate, with numerous strong spines; anal with 2 spines only. Ventral fins with 1 spine and 5 soft rays.

Small fishes of the tropical and warm seas, resembling the Chaetodontidae in form and mode of life, likewise usually of brilliant coloration; in structural characters intermediate between the Cichlidae and the Labridae. They feed chiefly on small marine animals, but the species with incisor-like teeth are entirely or mainly herbivorous. Over 150 species are known.

Principal genera: _Heliastes_, _Azurina_, _Amphiprion_, _Premnas_, _Dascyllus_, _Pomacentrus_, _Glyphidodon_, _Microspathodon_.

{673}The family is supposed to be represented in the Upper Eocene and Lower Miocene of Italy by the extinct genus _Odonteus_.

FAM. 35. LABRIDAE.—No subocular shelf; entopterygoid present; palate toothless; anterior teeth of the jaws usually strong and canine-like, lateral teeth often soldered at the base; lower pharyngeals completely united into one bone, with conical or tubercular teeth. Vertebrae with transverse processes from the third; all the ribs attached to the transverse processes. Lips thick. Two nostrils on each side. Gill-membranes free or joined to the narrow isthmus; 5 or 6 branchiostegal rays; gills three and a half; pseudobranchiae present. Dorsal fin elongate, with numerous, usually slender, spines. Ventral fins with 1 spine and 5 soft rays.

The "Wrasses" form a large family of mostly brilliantly coloured marine fishes, inhabiting all the tropical and temperate coasts. Their regime is partially herbivorous, partially carnivorous. About 400 species are known. Principal genera: _Labrus_, _Tautoga_, _Malacopterus_, _Ctenolabrus_, _Chaerops_, _Platychaerops_, _Heterochaerops_, _Labrichthys_, _Cossyphus_, _Cirrhilabrus_, _Chilinus_, _Epibulus_, _Anampses_, _Platyglossus_, _Novacula_, _Julis_, _Gomphosus_, _Chilio_, _Coris_.

Some of the members of this family have been observed to build nests for the protection of their eggs and young. These nests, in the European _Labrus_, are made of seaweeds, zoophytes, corals, broken shells, etc., and are the work of both the male and the female.[719] It is also in this family that sleep was first observed in fishes, and this has been fully verified by Möbius[720] {674}on _Labrus rupestris_ in an aquarium, the fish seeking a sleeping place at night and laying itself down to rest on one side.

As first pointed out by Günther, the Labridae found in temperate regions have a higher number (30 to 41) of vertebrae than those inhabiting the tropics (23 to 29), a rule which applies more or less to other families of Acanthopterygians. Remains of _Labrus_ and _Julis_ occur in the Eocene and Miocene of Europe. An allied fossil genus, _Labrodon_, is represented by numerous species in Tertiary beds of Europe and North America. _Phyllodus_, _Egertonia_, _Platylaemus_, and _Pseudosphaerodon_, from the Eocene and Miocene, are referred, with doubt, to this family.

FAM. 36. SCARIDAE.—Closely allied to the preceding, with which they have usually been united, but differing in the more or less coalescent teeth, forming often a parrot-like beak, the lower pharyngeals united into a concave or spoon-shaped bone with flat, tessellated teeth; and in the development of transverse processes from the first vertebra. Vertebrae 24 or 25.

Curious, mostly brilliantly-coloured fishes of the tropical seas and the Mediterranean, especially abundant about coral-reefs. "Parrot-Wrasses" feed mostly on vegetable matter, corals, and on hard-shelled Mollusca, for crushing which their dentition is well adapted. The largest reach a length of 4 feet. Some are much valued as food, whilst others are reputed poisonous. About 110 species are known, referable to 8 genera: _Cryptotomus_ (_Calliodon_), _Calotomus_, _Sparisoma_, _Scarus_, _Pseudoscarus_, _Odax_, _Coridodax_, _Siphonognathus_. The latter is very aberrant in shape, the head and body resembling those of a Pipe-Fish.

_Scarus_ is reported from the Eocene and Miocene of Europe.

{675}DIVISION II.—SCOMBRIFORMES.

No bony stay for the praeopercle. Spinous dorsal, if distinct, formed of short or feeble, slender spines. Epipleurals usually attached to the centra when ribs are sessile, or to the parapophyses of the vertebrae, rarely to the ribs. Pectoral arch similar to that of the Perciformes, but pterygials sometimes more abbreviated. Ventral fins thoracic. Caudal fin, if well developed, with very numerous rays deeply forked at the base.

Although bound by natural ties, the series of families that cluster round the Mackerel offer so many modifications of structure that it is almost impossible to draw up a diagnosis differentiating every one of its members from the Perciformes, with which they are closely connected, and from which they hardly deserve to be separated. Even after removing many genera which have been united with them by my predecessors, and which will now be found scattered among various groups of the system, no good definition of the Scombriformes can be given. The Mackerel and Horse-Mackerel are taken as the pattern-forms around which more or less aberrant types are located, types yet not so aberrant as to be traced back to these familiar forms through a number of intermediate grades. As {676}regards external features, it may be stated that the dorsal and anal spines, if present, are either weak and slender, or, if strong, short and detached; the caudal peduncle is constricted, and the caudal fin, if well developed, is usually deeply forked, and with the forked bases of the very numerous rays much longer than in most of the Perciformes, embracing at least a considerable portion of the expanded hypural bones, a character by which the Chaetodontidae, Acanthuridae, and several extinct types which have been placed with the Carangidae are at once excluded. All are carnivorous and marine, and many are pelagic and of very wide distribution. No praetertiary members of this division, as here defined, have yet been found.

SYNOPSIS OF THE FAMILIES

I. Praemaxillaries more or less protractile, not beak-like; scales small
or absent, sometimes with enlarged lateral scutes; spinous dorsal
fin short or replaced by a series of isolated spines; anal usually
with one or two spines detached from the rest of the fin.

Praecaudal vertebrae with transverse processes behind which the ribs
are attached 1. _Carangidae_.

Praecaudal vertebrae without well-developed parapophyses, ribs and
epipleurals inserted close together on the centra
2. _Rhachicentridae_.

II. Praemaxillaries not protractile; scales usually small or absent;
body more or less elongate; dorsal fin elongate, single or divided,
without free spines; no free anal spines.

A. Pseudobranchiae present.

Vertebrae without transverse processes; soft dorsal fin longer than
the spinous; pectoral fins high up the sides 3. _Scombridae_.

Vertebrae without transverse processes; soft dorsal fin shorter than
the spinous, if the latter be distinct; pectoral fins low down
the sides 4. _Trichiuridae_.

Vertebrae without transverse processes; snout produced into a spear
5. _Histiophoridae_.

Vertebrae with transverse processes bearing the ribs; snout produced
into a sword; no ventrals 6. _Xiphiidae_.

Vertebrae without transverse processes; gill-membranes attached to
isthmus; dorsal and anal fins formed of unarticulated, widely set
rays; dentition very feeble 7. _Luvaridae_.

B. Pseudobranchiae absent; no well-developed transverse processes to
the praecaudal vertebrae; the ribs and the epipleurals inserted
close together on the centra; snout short and very deep
8. _Coryphaenidae_.

III. Praemaxillaries not protractile, or if slightly protractile,
scales large; dorsal and anal fins elongate, without distinct spinous
division; most of the praecaudal vertebrae with strong haemapophyses,
to which the ribs are attached 9. _Bramidae_.

{677}FAM. 1. CARANGIDAE.—Praemaxillaries more or less protractile. Vertebrae 24 to 26; ribs behind the parapophyses; epipleurals on the parapophyses, rarely on the ribs.[721] Body covered with small scales, or naked, often with enlarged scutes on each side of the body or of the tail; dorsal spines few, or slender or rudimentary; a more or less developed spine adnate to the soft portion of the anal, often preceded by a pair of spines separated from the rest of the fin. Pseudobranchiae usually present. Inhabitants of the seas of the temperate and tropical regions, many of the species having a very wide range. About 150 species are known.

Principal recent genera: _Caranx_, _Chloroscombrus_, _Selene_, _Mene_, _Apolectus_, _Nematistius_, _Seriola_, _Seriolichthys_, _Naucrates_, _Trachynotus_, _Zalocys_, _Lichia_, _Paropsis_, _Chorinemus_. Species of _Caranx_, _Mene_, and _Seriola_ have been described from the Eocene and Miocene of Europe, in which occur also the fossil genera named _Vomeropsis_, _Archaeus_, _Carangopsis_, _Carangodes_, _Ductor_, and _Semiophorus_.

The family is represented on our coasts by the common Horse-Mackerel, _Caranx trachurus_. The young of this species keep together in small bands in the neighbourhood of medusae, under which they seek shelter when disturbed. The Pilot-Fish, _Naucrates ductor_, is a truly pelagic fish of wide distribution, which occasionally appears on our coasts, accompanying large sharks and ships. Much has been written on the marvellous habits of this little fish, which is said to lead the shark like a pilot, directing it to its food, in exchange for which services the pilot enjoys protection from the fear which the proximity of its formidable companion inspires to its enemies among other carnivorous fishes, and an abundance of food from the shark's excrements.[722]

FAM. 2. RHACHICENTRIDAE.—Praemaxillaries slightly protractile. Vertebrae 25 (11 + 14), without well-developed parapophyses; ribs and epipleurals inserted close together on the centra. Body covered with very small scales; a series of short isolated dorsal spines; soft dorsal and anal long; pectorals {678}inserted low down. A single genus, _Rhachicentrum_ (_Elacate_), with a single species from the coasts of the tropical and warmer parts of the Atlantic and of the Indian Ocean.

FAM. 3. SCOMBRIDAE.—Praemaxillaries large, not protractile, beak-like. Vertebrae 30 to 50, without transverse processes, but some of the hinder praecaudals with haemal arches; ribs inserted on the centra or on the haemal arches when these are present; epipleurals all on the centra. Scales cycloid and usually very small (except in _Gastrochisma_), sometimes absent. A spinous dorsal fin formed of slender spines, folding into a sheath; soft dorsal longer and broken up into finlets, similar to the anal; pectoral inserted high up the sides. Hypural bones completely embraced by the forked bases of the caudal rays. Pseudobranchiae present.

About 50 species, referred to the following genera:—_Scomber_, _Auxis_, _Thunnus_, _Sarda_, _Cybium_, _Acanthocybium_, _Gastrochisma_ (_Lepidothynnus_). Numerous fossil representatives in Tertiary beds, belonging to _Scomber_, _Auxis_, _Thunnus_, _Cybium_, and to the extinct genera _Eothynnus_, _Isurichthys_, _Palimphyes_, _Scombrinus_, _Sphyraenodus_, _Scombramphodon_.

These fishes, elegant in form and often in colour, are among the swiftest of the inhabitants of the sea. Some are migratory, like the Mackerel (_Scomber scombrus_) of the North Atlantic, whilst others are remarkable for their wide distribution. The Tunny (_Thunnus thynnus_), for instance, the largest member of the family, reaching a length of 10 feet, inhabits the Atlantic, Pacific, and Indian Oceans, extending as far north as the British {679}seas, Newfoundland, California, and Japan. It supplies important fisheries in France and Italy. The Tunnies are the only fish known to be warm-blooded.

FAM. 4. TRICHIURIDAE.—Praemaxillaries not protractile. Vertebrae 32 to 160, without transverse processes; ribs sessile, on the centra or on the haemal arches when these are present; epipleurals, if well developed, on the centra. Scales very small or absent. Spinous portion of dorsal fin much longer than the soft, the spines more or less feeble. Pectoral fins inserted low down the sides. Pseudobranchiae present.

The members of this family show a great variation in the shape of the body, which, although always strongly compressed, is not unlike that of a Mackerel in the more normal types, such as _Thyrsites_ and _Ruvettus_, whilst, through a chain of genera, it generally assumes an extremely elongate form; concurrently with this elongation of the body, the dorsal fin loses its differentiation into two portions, the ventrals become reduced and disappear, as in the Scabbard- or Frost-Fish (_Lepidopus caudatus_), while the caudal fin decreases in size, loses its fork-shape, and is finally lost in _Trichiurus_, in which the body is ribbon-shaped and tapers to a point.

About 25 species are known, pelagic and widely distributed, many descending to great depths.

Principal living genera: _Ruvettus_, _Thyrsites_, _Epinnula_, _Nesiarchus_, _Nealotus_, _Promethichthys_, _Dicrotus_, _Gempylus_, _Aphanopus_, _Lepidopus_, _Euoxymetopon_, _Benthodesmus_, _Eupleurogrammus_, _Trichiurus_.

Remains of several species referred to _Thyrsites_, _Lepidopus_, and to the extinct genera _Thyrsitocephalus_, _Hemithyrsites_, and _Trichiurichthys_, have been found in the Oligocene and Miocene of Europe.

FAM. 5. HISTIOPHORIDAE.—Praemaxillaries not protractile; snout produced into a spear-shaped rostrum; a praedentary bone; teeth minute. Body elongate, covered with small or rudimentary scales. Vertebrae 24 or 25, without transverse processes; ribs sessile; no epipleurals. One or two dorsal fins, without a distinctly spinous portion. Pectoral fin low down the side. Pseudobranchiae present.

The Sail-Fishes are large oceanic fishes, endowed with great strength and swiftness, occurring in the tropical and sub-tropical {680}seas. Four or five species are distinguishable, and are referable to two genera: _Histiophorus_, with a single dorsal fin and 2 or 3 ventral rays, and _Tetrapturus_, with the dorsal divided into two parts and a single ventral ray.[723]

Fossil Histiophoridae are known from the Eocene and later beds in Europe and America. Dr. A. S. Woodward observes that the known fossils are too imperfect to be referred with certainty to their respective genera. Most of them probably belong to _Histiophorus_, but at least one genus from the Eocene (_Xiphiorhynchus_) appears to be well distinguished.

The imperfectly known extinct family PALAEORHYNCHIDAE, from the seas of the Eocene, Oligocene, and Miocene periods, with the genera _Palaeorhynchus_ and _Hemirhynchus_, is probably closely related to the Histiophoridae. The vertebrae number 50 to 60, and the ribs completely encircle the body. In _Palaeorhynchus_ both jaws are equally produced into an ensiform weapon. _Blochius_, from the Eocene, with diamond-shaped, slightly overlapping bony scutes on the body, is perhaps also to be placed near this family.

{681}FAM. 6. XIPHIIDAE.—Differs from the preceding in the absence of praedentary bone, and in the vertebrae (26 in number), which in the praecaudal region are provided with short but well-developed transverse processes, to which the short ribs are attached. Ventral fins absent, the pectorals being inserted in the place usually occupied by them. Adult without teeth or scales.

A single species, the Sword-Fish (_Xiphias gladius_), of nearly world-wide distribution, occurring occasionally on the coasts of Great Britain and Ireland.

FAM. 7. LUVARIDAE.—Mouth small, praemaxillaries not protractile, with very feeble dentition. Gill-membranes attached to the isthmus. Vertebrae 23, without transverse processes; ribs blade-like, inserted on the centra; no epipleurals. Body rough, with minute scales. Dorsal and anal fins elongate, formed of unarticulated, widely set rays. Pectoral fins inserted rather low down; ventrals much reduced, the two halves of the pelvis fused into a single bone. Supraclavicle fused with the forked post-temporal. Hypural bones completely embraced by the forked bases of the caudal rays. Pseudobranchiae present.

_Luvarus imperialis_, a rare pelagic fish from the Atlantic, Mediterranean, and Pacific, growing to a length of 6 feet, and occasionally captured on our coasts, is the only representative of this family. Very little is known of the habits of this strange fish. The excessive length of the intestines and the feeble dentition point to its feeding partly on vegetable matter, partly on minute animals; the circumstances under which certain specimens were captured tend to indicate that they follow up streams of pelagic life such as engage the attention of the Basking Shark, of similar distribution.

FAM. 8. CORYPHAENIDAE.—Praemaxillaries small, not protractile. Vertebrae 30 to 33, without transverse processes; ribs and epipleurals attached close together on the centra. Body elongate; scales small, cycloid or elongate lanceolate. Dorsal and anal fins much elongate, without distinct spines. Pectoral fins inserted rather low down the side. Pseudobranchiae absent.

The "Dolphins" (_Coryphaena_), of which only two species can be distinguished, are large pelagic fishes, of carnivorous habits, pursuing the Flying-Fish. They grow to a length of 6 feet, and their flesh is much valued. Their deep head, with short snout, {682}and their long posteriorly attenuate body ending in a large forked caudal fin, give them a peculiar appearance.

FAM. 9. BRAMIDAE.—Praemaxillaries small, not or but feebly protractile; maxillaries large, scaly. Vertebrae 42 to 47, the praecaudal without transverse processes, but mostly with hæmal arches to which the ribs are attached, the epipleurals being inserted on the centra. Body deep; scales moderate or large, strongly imbricate, with processes which, in certain parts at least, serve to connect the rows of scales. Dorsal and anal elongate, some or all of the rays simple, but not forming true spines. Pectoral inserted rather low down the side, freely movable upwards and downwards. Pseudobranchiae present.

Pelagic fishes, often descending to great depths. About 12 species are known,[724] referable to 6 genera: _Brama_, _Taractes_, _Pterycombus_, _Pteraclis_, _Bentenia_, and _Steinegeria_. _Taractes_, often confounded with _Brama_, differs from it not only in the larger, keeled scales, but also in the protractile mouth and in the much greater development of most of the ribs, which form curved lamellae of great width.[725] _Pteraclis_ is very remarkable for the enormous, sail-like dorsal and anal fins.

DIVISION III.—ZEORHOMBI.

Aberrant, strongly compressed Perciformes, with very short praecaudal region, modified much as in the Flat-Fishes, culminating in asymmetrical forms, and characterised by the combination of an increased number (7 to 9) of ventral rays, with absence of hypural spine (by which the Berycidae are excluded), _or_ by asymmetry of the skull in the forms in which the spine of the ventral fin has been lost.

Among the symmetrical forms, the existing Zeidae agree with the Berycidae in having more than five soft rays to the ventral fins, and are probably derived, together with the Eocene Amphistiidae, from some common ancestral group still to be discovered in Cretaceous beds. These Zeidae have much in common with the Pleuronectidae,[726] and might be regarded as {683}forming part of the family out of which the latter have sprung, were it not that they have lost the last half-gill. _Amphistium_ is probably more nearly related to the Pleuronectidae, which may have been directly derived from the family of which it is as yet the only known representative.[727]

This division embraces three families only:—

A distinct spinous dorsal fin; anal spines detached from the soft
portion; a ventral spine; gills three and a half, four slits between
them 1. _Zeidae_.

Dorsal and anal spines few, continuous with the soft rays; a ventral
spine 2. _Amphistiidae_.†

No spines; cranium twisted in front, with the two orbits on one side;
gills 4, a slit behind the fourth 3. _Pleuronectidae_.

† Extinct.

FAM. 1. ZEIDAE.—No subocular shelf; praemaxillaries strongly protractile. Gill-membranes free from isthmus; 7 or 8 branchiostegal rays; gills 3½; pseudobranchiae well developed. Lower pharyngeal bones separated. Vertebrae 30 to 46, the anterior with sessile ribs, the posterior praecaudals with long neural spines bent forwards and with transverse processes directed downwards, forming haemal arches and bearing the ribs at their extremity; epipleurals much reduced or absent; hypural large, without the basal spine or knob present in most Perciformes and all Scombriformes and Percesoces, bearing fewer than 20 rays. Dorsal and anal fins elongate, the former with a distinct spinous portion, the latter with 1 to 4 spines detached from the soft portion. Pectoral fin supported by 4 pterygials, of which 3 are in contact with the perforated scapular bone; post-temporal forked and solidly attached to the skull. Ventral fin with 1 spine and 6 to 8 soft rays.

Scales small or minute, sometimes hard and rough and firmly joined in vertical series; bony plates may be present along the base of the vertical fins. Air-bladder present.

Twelve species are known from the Atlantic and Pacific Oceans, referable to 5 genera: _Grammicolepis_, _Cyttus_, _Cyttopsis_, _Zenion_, and _Zeus_. _Oreosoma_ was founded on a young form of a fish allied to _Cyttus_. Remains of _Zeus_ occur in the Oligocene, and _Cyttoides_, from the same period, has been compared with _Cyttus_.

The well-known John Dory (_Zeus faber_) is much valued for the table.

{684}FAM. 2. AMPHISTIIDAE.—The only known representative of this family, the Upper Eocene _Amphistium paradoxum_, originally described as a _Pleuronectes_, has much in common with the Zeidae, from which it differs in the smaller number of vertebrae (10 + 14), and in the dorsal and anal spines being more reduced, adnate and continuous with the series of soft rays; the scales are more normal and imbricate; ventral fins with 1 spine and 8 soft rays. This fish appears to realise in every respect the prototype of the Pleuronectidae before they had assumed the asymmetry which characterises them as a group.

FAM. 3. PLEURONECTIDAE.—Head asymmetrical, the skull twisted in front, with the two orbits on one side in the adult; the side of the body bearing the eyes and turned upwards in life being coloured, the other side colourless and blind. Mouth more or less protractile. Gills 4, a slit behind the fourth; pseudobranchiae present. Lower pharyngeal bones usually separated, rarely imperfectly united. Vertebrae 24 in the most generalised form (_Psettodes_), varying from 28 to 65 in others, the praecaudals mostly with more or less developed transverse processes, which may be directed downwards and become converted into haemal arches; ribs and epipleurals present. Caudal fin, if well developed, supported by a large hypural usually without basal spine or knob. Dorsal and anal fins much elongate, without spines, the former often extending on the head. Paired fins often reduced, {685}sometimes absent; if fully developed and normally formed, the bones of the pectoral and pelvic girdles as in the Zeidae. Ventral fins usually with 5 to 7 soft rays.

Scales usually imbricate, cycloid or ctenoid; rarely absent; bony tubercles sometimes present. Air-bladder absent.

Most species, and even genera, are either sinistral or dextral, but this is inconstant in some, including the most generalised genus, _Psettodes_. The very young are transparent and symmetrical, with an eye on each side, and swim in a vertical position like other Fishes. These larval forms have been described as distinct genera, under the names of _Peloria_, _Bibronia_, _Charybdia_, etc. As they grow, the eye of one side moves by degrees to the other side, where it becomes the upper eye. If at that age the dorsal fin does not extend to the frontal region, the migrating eye simply moves over the line of the profile, temporarily assuming the position which it preserves in _Psettodes_, _Atheresthes_, and _Platysomatichthys_; in other genera, the dorsal fin has already extended to the snout before the migration takes place, and the eye, passing between the frontal bone and the tissues supporting the fin, appears to pass from side to side through the head, as was believed by some of the earlier observers.[728]

Flat-fishes are a large group of some 500 species, mostly marine, a few species related to the Soles being confined to the fresh waters of South America and the Malay Archipelago. They range from the Arctic Circle to the southern coasts of the Southern Hemisphere; many occur at great depths (_Citharichthys dinoceros_ down to 955 fathoms). Well-preserved remains referred to _Psetta_ occur in the Upper Eocene, and a species of _Solea_ is known from the Lower Miocene.

{686}

{687}A satisfactory classification of the Pleuronectidae is still a desideratum, and cannot be attempted until the osteology of the very numerous forms has been thoroughly studied. Even the division into two principal groups, regarded by some recent authors as families, Pleuronectidae and Soleidae, is based on characters which the examination of a large number of generic types shows not to be constant. Thus the former have been defined as having the praeopercular margin distinct externally, the snout not projecting beyond the mouth, the nostrils of the two sides on the coloured side or those of the blind side high up near the dorsal line of the head; the latter as having the praeoperculum hidden under the skin, the snout projecting more or less beyond the mouth, and the nasal organ of the blind side similarly situated to that of the eyed side. However, the genera _Aphoristia_ and _Peltorhamphus_, and others among the Soles, show exceptions to this definition.[729]

Principal genera: _Psettodes_, _Atheresthes_, _Platysomatichthys_, _Hippoglossus_, _Hippoglossoides_, _Hippoglossina_, _Poecilopsetta_, _Chascanopsetta_, _Paralichthys_, _Pleuronectes_, _Glyptocephalus_, _Citharus_, _Rhomboidichthys_, _Psetta_ (_Rhombus_), _Arnoglossus_, _Zeugopterus_, _Lepidorhombus_, _Ammotretis_, _Rhombosolea_, _Solea_, _Achirus_, _Achiropsis_, _Soleotalpa_, _Synaptura_, _Ammopleurops_, _Aphoristia_, _Cynoglossus_, _Symphurus_ (_Plagusia_).

The following are the principal British representatives which are valued as food:—The Halibut (_Hippoglossus vulgaris_), by far the largest of all Flat-Fishes, growing to a length of 10 feet or more; the Long Rough Dab (_Hippoglossoides limandoides_); the Plaice (_Pleuronectes platessa_); the Flounder (_P. flesus_), which ascends streams; the Dab (_P. limanda_); the Smear Dab, often called Lemon Sole (_Glyptocephalus microcephalus_); the Witch (_G. cynoglossus_); the Megrim or Whiff (_Lepidorhombus megastoma_); the Turbot (_Psetta maxima_); the Brill (_P. laevis_); and the Sole (_Solea vulgaris_).

DIVISION IV.—KURTIFORMES.

No bony stay for the praeopercle. Dorsal spines feeble, few. Scapula absent, the coracoid supporting four small pterygials. Ventral fins thoracic.

FAM. 1. KURTIDAE.—The genus _Kurtus_, with a single species, from the Indian and Pacific Oceans, forms an isolated, very {688}aberrant group. The strongly compressed body is covered with minute, rudimentary scales; the dorsal is short, with few, graduated spines, and the anal much elongate, with 2 small spines; the ventrals are formed of 1 spine and 5 soft rays. The vertebral column consists of 24 vertebrae; the ribs of the third and fourth are free and slender, whilst the following are immovably fixed between rings formed by the ossification of the outer membrane of the elongate air-bladder in a manner unique among fishes. The skull is peculiar for its very strong, denticulate, occipital crest, which ends posteriorly in a curved spine bent forwards; the suborbitals are slender and do not emit a subocular lamina. _Kurtus indicus_ does not exceed a length of 5 inches.

DIVISION V.—GOBIIFORMES.

No bony stay for the praeoperculum. Basis cranii simple. Spinous dorsal, if present, formed of few, flexible rays. None of the epipleural bones attached to the centra of the vertebrae in the praecaudal region. Scapula and coracoid more or less reduced or even vestigial; pterygials large, 4 or 5 in number, forming together a thin plate which is in contact with or narrowly separated from the clavicle; one or two of the pterygials in contact with the coracoid. Ventral fins thoracic.

The Gobiidae, which alone constitute this division, are not very remote from the Perciformes, and may have evolved out of a type not very different from the Percidae.

{689}FAM. 1. GOBIIDAE.—Suborbital arch ligamentous or absent. Gill-membranes more or less broadly attached to isthmus; 4 to 6 branchiostegal rays; gills 4, a slit behind the fourth; pseudobranchiae often present. All or most of the praecaudal vertebrae with transverse processes bearing the ribs, to which epipleurals are attached. Post-temporal forked, as in normal Perciformes. Ventral fins with 1 feeble spine and 4 or 5 branched rays, often united to form a sucking disk, a transverse fold of skin at their base completing the cup.

Head usually more or less depressed, body varying from short and stout to elongate and eel-shaped, but never with a very high number of vertebrae, these varying from 24 to 37 (10-14 + 13-24); scales cycloid or ctenoid, or absent; no lateral line; mouth moderate or large, dentition various; soft dorsal and anal fins nearly equally developed, varying from very short to very elongate; usually a large anal papilla.

A large family of some 600 species, the great majority marine, mostly carnivorous and of small size. The largest form (_Eleotris marmorata_, from the rivers of Siam, Borneo, and Sumatra) grows to nearly 3 feet, whilst the smallest (_Mistichthys luzonensis_, from the Philippines) measures only 12 to 14 millimetres, and is believed to be the smallest known Vertebrate. Gobiids occur in all the seas outside the Arctic and Antarctic circles, and they have representatives in the fresh waters of all parts of the world.

The genera are numerous but difficult of definition. The following are the principal: _Eleotris_, _Oxymetopon_, _Vireosa_, _Rhyacichthys_, _Gobius_, _Crystallogobius_, _Aphia_, _Gobiosoma_, _Gobiodon_, _Benthophilus_, _Typhlogobius_, _Luciogobius_, _Sicydium_, _Lentipes_, _Periophthalmus_, _Boleophthalmus_, _Amblyopus_, _Trypauchen_, {690}_Trypauchenichthys_. _Oxuderces_, which has been made the type of a distinct family, appears to differ from _Trypauchen_ only in the absence of ventral fins. Fossils referred to _Gobius_ have been described from the Upper Eocene and Miocene of Europe, but there is no satisfactory evidence that they really belong to this family.