Chapter XXIII: Appendix: To the Fishes: Palaeospondylidae—ostracodermi—heterostraci (4)

FAM. 2. HALOSAURIDAE.—Body elongate, covered with cycloid scales, the tail tapering to a point, without caudal fin; head with scales; mouth moderate, bordered by the praemaxillaries and the maxillaries, both toothed; suborbitals large; praeopercle rudimentary. Dorsal fin short, formed of soft rays, above or a little behind the ventrals, which are rather far back, and formed of 9 or 10 rays; anal very long, without spines, extending to the end of the tail. Ovaries transversely laminated, the ova falling into the abdominal cavity. Some 10 living species are known, referred to three genera, inhabiting the Atlantic, Pacific, and Indian Oceans, at depths of 500 to 1400 fathoms.

{624}In _Halosaurus_ the scales of the lateral line, which runs near the lower profile, are scarcely enlarged, and are destitute of luminous organs. _Halosaurichthys_ differs in the union of the ventral fins with each other, as in _Notacanthus_. In _Halosauropsis_ the scales of the lateral line are strongly enlarged and pouch-like, and bear photophores.

This family is one of great antiquity, being represented in the Upper Cretaceous of Westphalia by _Echidnocephalus_, which, as shown by A. S. Woodward, appears to have been closely related to _Halosaurus_.

FAM. 3. LIPOGENYIDAE.—Similar to the preceding in shape and in the position of the dorsal fin, but with a toothless, roundish, inferior, suctorial mouth, and with the short dorsal and the long anal formed partly of spines and partly of soft rays. Head and body covered with minute scales; lateral line nearer the dorsal than the ventral profile. Ventrals with 3 spines and 7 soft rays. A single species, _Lipogenys gillii_, from the North Atlantic, 865 fathoms.

FAM. 4. NOTACANTHIDAE.—Body elongate, covered with very small cycloid scales, the tail tapering to a point, without caudal fin; head scaly; mouth small, inferior, bordered by the praemaxillaries only; jaws toothed; no suborbitals; praeoperculum small; post-temporal replaced by ligament. Dorsal fin formed of a series of short disconnected spines; anal very long, formed partly of spines and partly of soft rays, extending to the end of the tail. Ventrals with 1 to 5 spines and 7 to 10 soft rays.

{625}Two genera: _Notacanthus_, with the ventrals connate or confluent and with 6 to 12 dorsal spines; and _Polyacanthonotus_, with the ventrals separated and 27 to 38 dorsal spines. Nine species, from the Mediterranean, the Atlantic, and the Pacific, at depths of 400 to 1875 fathoms.

FAM. 5. FIERASFERIDAE.—Body elongate or extremely attenuate, naked, the tail tapering to a point or truncate, without distinct caudal fin; mouth small, inferior, bordered by the praemaxillaries; jaws toothed; no suborbitals; praeoperculum well developed. Dorsal and anal fins very long, extending to the end of the tail, and formed entirely of soft rays. Ventral fins absent. Vent situated immediately behind the gill-opening. Air-bladder with a muscular apparatus for dilatation of its anterior part.

A single genus, _Fierasfer_, with about 10 species, distributed over nearly all the warm and tropical seas, rarely found as far north as the west coast of Ireland. _Encheliophis_, without pectoral fins, is the larval form of _Fierasfer_.

_Fierasfer_ spends the greater part of its existence in the interior of Holothurians and other Echinoderms as well as in bivalve Mollusca. It has been observed to enter Holothurians by the posterior or anal aperture, either head first or tail foremost, in the latter case availing itself of the suction which takes place alternately with the expulsion of water by that orifice; it remains near the anus, from which it projects its head in search of food outside its host. It is neither a true parasite nor a commensal or mutualist, in the sense given to these terms by Van Beneden, but simply a lodger, "inquilino," as Emery puts it. Semper, however, regards _Encheliophis vermicularis_ as a true parasite, feeding on the viscera of the Holothurian in which it lives. Putnam has examined eight specimens of a _Fierasfer_ from the Bay of Panama, which were obtained alive from pearl oysters, and also one beautifully {626}enclosed in a pearly covering deposited upon it by the oyster; a similar specimen is preserved in the British Museum.

SUB-ORDER 7. CATOSTEOMI.

Air-bladder, if present, without open duct. Parietal bones, if present, separated by the supraoccipital. Pectoral arch suspended from the skull; no mesocoracoid arch; coracoid usually very large. Ventral fins, if present, abdominal, or pelvis attached to the coracoid bones.

The mouth is small and bordered by the praemaxillaries or by the praemaxillaries and a small portion of the maxillaries. The air-bladder is present, except in the Solenostomidae and Pegasidae.

Following the suggestions of Kner and Steindachner and Cope to their logical conclusion, A. S. Woodward, in his valuable catalogue of the Fossil Fishes in the British Museum, has united the Lophobranchs of Cuvier with the Hemibranchs of Cope, a course which seems fully justified, and has received {627}further support from the recent investigations of Swinnerton,[698] who has proposed to unite the two groups under the new name of Thoracostei. The name Phthinobranchii has also been suggested by O. P. Hay for the same association. The structure of the Lophobranchs (Solenostomidae and Syngnathidae) shows that these fishes are only extremely specialised forms of the group of which the Sticklebacks are the well-known type, and the character of the "tufted" gills alone is surely not of sufficiently great importance to warrant the retention of the Lophobranchii as a division equivalent to the sub-orders adopted in the present classification. Besides, as recently pointed out by A. Huot,[699] there is no fundamental difference, but only one of degree, between the so-called tufted gill and the normal type; each "tuft" corresponds to one branchial lamella, and at a certain stage of development the disposition of the branchial lamella is the same in a _Syngnathus_ and in an ordinary Teleostean. I have recently attempted to show[700] that the Lamprididae are related to the Hemibranchii, although sufficiently distinct to warrant the establishment of a division, named Selenichthyes.[701]

SYNOPSIS OF THE FAMILIES.

I. Praeoperculum and symplectic distinct; branchial apparatus fully
developed; gills pectinated; mouth terminal, toothless; post-temporal
forked, free; pelvic bones connected with scapular arch; ventral fins
with 15 to 17 rays; ribs long, sessile; fins without spines
(SELENICHTHYES) 1. _Lamprididae_.

II. Praeoperculum and symplectic distinct, latter much elongate;
branchial apparatus more or less reduced; gills pectinate;
post-temporal simple, immovable; mouth terminal (HEMIBRANCHII).

A. Mouth toothed.

1. Pelvic bones usually connected with scapular arch; spinous dorsal
represented by isolated spines.

Snout conical or but slightly tubiform; ventral fins with
1 spine and 1 or 2 soft rays; ribs slender, free; anterior
vertebrae not enlarged 2. _Gastrosteidae_.

Snout tubiform; ventral fins with 1 spine and 4 soft rays; {628}
ribs flattened, fused with the lateral bony shields;
anterior vertebrae not enlarged 3. _Aulorhynchidae_.

Snout tubiform; ribs slender, free; first vertebra enlarged
4. _Protosyngnathidae_.

2. Pelvic bones not connected with scapular arch; ventrals without
spine, with 5 or 6 rays; snout tubiform; first vertebra very
elongate, formed by the fusion of several.

Isolated dorsal spines; body scaly 5. _Aulostomatidae_.

No dorsal spines; body naked 6. _Fistulariidae_.

B. Mouth toothless; snout tubiform; two short dorsal fins, the first
with a few spines; ventral fins with 3 to 5 rays; anterior
vertebrae elongate.

Body covered with bony shields and small rough scales
7. _Centriscidae_.

Body completely cuirassed by bony shields which are fused with the
endoskeleton 8. _Amphisilidae_.

III. Praeoperculum absent; symplectic much elongate; branchial
apparatus more or less reduced; gill-lamellae reduced in number and
enlarged, forming rounded lobes; post-temporal simple, immovably
attached to the skull; mouth toothless, at the end of a tubiform
snout; body covered with bony plates (LOPHOBRANCHII).

Two dorsal fins; ventral fins present, with 7 rays; gill-openings
wide; exoskeleton of large star-like plates 9. _Solenostomidae_.

A single dorsal fin; no ventral fins; gill-openings very small;
exoskeleton in the form of rings 10. _Syngnathidae_.

IV. Praeoperculum and symplectic absent; gills pectinated; mouth
inferior, toothless; body entirely covered with bony plates; ventral
fin with 2 or 3 rays (HYPOSTOMIDES) 11. _Pegasidae_.

FAM. 1. LAMPRIDIDAE.—Body short and deep, with minute scales. Snout short; mouth toothless, bordered by the praemaxillaries and, to a small extent, by the maxillaries; opercular bones well developed. Gills four, pectinated; branchial apparatus fully developed. Post-temporal bone forked. Vertebrae very numerous (21 + 25), without transverse processes; ribs strong, long. Fins without spines; dorsal and anal elongate. Pectoral fins with very short pterygials folding downwards against the body. Pelvic bones connected with the coracoids, which are very large, and do not form a suture at their ventral extremity. Ventral fins with 15 to 17 rays.

The Opah or King-Fish (_Lampris luna_), the sole representative of this family, is remarkable for its large size (growing to a length of four feet) and its vivid colours. Its flesh is rich, and intermediate between that of the Salmon and that of the Tunny. It is a pelagic fish of wide distribution, known from the North {629}Atlantic and Mediterranean and from distant points in the Pacific; specimens are occasionally captured on our coasts. It feeds on other fish, but little is known of its habits and nothing of its development.

The affinities of the _Lamprididae_ are very doubtful. _Lampris_ has usually been placed with the Acanthopterygians, a view which is still upheld by Gill.[702] I now agree with this high authority in regarding the bone which I took for an infraclavicle as a much developed coracoid, and the bone termed by me the coracoid as a pterygial. But it has also been shown, by Starks, that such a thing as an infraclavicle does not exist in the Stickleback, the bone so-called being only a part of the coracoid; and as in most of the Sticklebacks the pelvic bones join the latter, the resemblance between them and _Lampris_ remains. As I have previously pointed out, the absence of spines in the fins, and the position of the ventral fins, together with the great number of rays in the latter, which is only met with in the lower Teleosteans, are characters which necessitate the removal of _Lampris_ from the Acanthopterygians, and I cannot find a better place for them than near the Gastrosteidae.

The whole question of the arrangement of the Physoclists with abdominal ventrals (Catosteomi and Percesoces) is, I feel, much in need of revision, and it may be found advisable to break up this group into a greater number of sub-orders, in which case the Selenichthyes would stand by themselves; the Hemibranchii and Lophobranchii would be united under the former name, as proposed by Woodward, or under that of Thoracostei (Swinnerton) or Phthinobranchii (Hay). The position in the system of the Pegasidae is still somewhat doubtful. This family is regarded by some authors as related to the mail-cheeked Acanthopterygians.

FAM. 2. GASTROSTEIDAE.—Body more or less elongate, naked or protected by bony shields, tapering to a slender caudal peduncle. Head moderate, with short or elongate and tubiform snout; mouth small, terminal, toothed; opercular bones well developed; suborbitals in contact with praeoperculum, protecting the cheek. Gills four, pectinated. Praecaudal vertebrae with strong transverse processes and slender, free ribs. Spinous dorsal represented by isolated spines. Pectoral fins with short {630}pterygials. Pelvic bones usually connected with scapular arch. Ventral fins with one spine and one or two soft rays.

Four genera: _Gastrosteus_, _Apeltes_, _Eucalia_, _Spinachia_.

The little Three-spined and Two-spined Sticklebacks (_Gastrosteus aculeatus_ and _G. pungitius_), which include many varieties that have been regarded as distinct species, are among the best known of our British Fishes. They are remarkable for the perfect indifference with which they can be transported from fresh into salt water, and _vice versa_, and for the elaborate nests which the males build in fresh or brackish water, and over which they watch with the greatest vigilance after the female has deposited her relatively large eggs.[703] These nests are made of weeds and twigs fastened together by threads secreted by the kidneys of the male. The {631}larger fifteen-spined Stickleback (_Spinachia vulgaris_) is entirely marine; its nests are to be found on our coasts in sheltered rock-pools, and they are made chiefly of sea-weeds and Hydrozoa. Sticklebacks are short-lived, and are believed to breed only once.

The Gastrosteidae are restricted to the northern hemisphere, being more abundant in the higher latitudes, extending to Iceland, Greenland, and Bering Straits; the southernmost points of their distribution are Algeria in the Old World, and Lower California in the New.[704]

A very large number of species have been described, but probably only about a dozen deserve to stand.

FAM. 3. AULORHYNCHIDAE.—The genera _Aulorhynchus_ and _Auliscus_, each with one species from the Northern Pacific, much resemble _Spinachia_ in outward form and in the equal size of the anterior vertebrae, but the snout is still more produced, tubiform, and the ventral fins are formed of one spine and four soft rays. The difference which justifies their separation as a distinct family resides in the disposition of the ribs, which are flattened and ankylosed to the lateral bony shields.

FAM. 4. PROTOSYNGNATHIDAE.—This family appears to be intermediate between the Gastrosteidae and the Aulostomatidae, agreeing with the former in possessing slender, free ribs, with the latter in having the first vertebrae elongate, though to a {632}less degree than in _Aulostoma_. Its only representative is _Protosyngnathus sumatrensis_, from a Tertiary freshwater formation in Sumatra, which has been referred, without adequate grounds, to _Aulorhynchus_ or _Auliscops_.[705]

FAM. 5. AULOSTOMATIDAE.—Allied to the Aulorhynchidae, differing in the ventral fins devoid of spines, formed of 5 or 6 rays, widely removed from the pectoral arch, the very elongate, saddle-shaped anterior vertebra formed by the fusion of several, the large supratemporals produced backward over the anterior vertebra, the very elongate pterygials of the pectoral fin, and the compressed body covered with small ctenoid scales. Ribs are rudimentary or absent. No suborbitals. The snout is long, tubiform; the small terminal mouth bears bands of minute teeth, and the lower jaw has a small barbel at the symphysis. A single genus, _Aulostoma_, with two species from the Atlantic coasts of tropical America, and two from the Eocene and Miocene of Europe. _A. coloratum_ grows to a length of 26 inches.

FAM. 6. FISTULARIIDAE.—Body greatly elongate, naked. First vertebra much elongate, formed by the fusion of several; strong transverse processes to the ribs in front and behind, those of two vertebrae suturally united; ribs rudimentary or absent. Supratemporal much produced posteriorly, extending over the anterior vertebrae; suborbitals absent; snout forming a long tube, which terminates in a narrow mouth with minute teeth. Spinous dorsal entirely absent. Pterygials of pectoral fin very elongate. Ventral fins very small, with 6 soft rays, inserted far behind the pectoral girdle.

The Flute-mouths, _Fistularia_, which Dr. Günther describes as "gigantic marine Sticklebacks living near the shore, from which they are frequently driven into the open sea," are represented by three species, from the tropical and subtropical parts of the Atlantic and Indo-Pacific. The middle rays of the forked caudal fin are produced into a long filament. The largest species, _F. tabaccaria_, reaches a length of 6 feet. The same genus is represented by two species in the Upper Eocene and Oligocene of Europe, and _Urosphen_, from the Upper Eocene, is regarded as allied to it.

{633}FAM. 7. CENTRISCIDAE.—Body moderately elongate, partially enclosed in a bony armour, which is distinct from the endoskeleton. Anterior vertebrae elongate, with strong parapophyses ankylosed to the exoskeleton; no ribs. Suborbitals absent; snout forming a long tube, with small, terminal, toothless mouth. Two dorsal fins, the anterior with a very strong spine. Pterygials of pectoral fin very small. Ventral fins small, with 4 or 5 rays, the pelvic bones in contact with the postclavicles.

_Centriscus_, with five species in the Atlantic and Pacific Oceans, represents this family at the present day. _C. scolopax_ has occasionally been found on the English coast. Isolated spines from the Pliocene of Tuscany have been referred to the same genus. _Rhamphosus_, from the Eocene of Monte Bolca, is believed to have been allied to _Centriscus_.

FAM. 8. AMPHISILIDAE.—Near the preceding, but body extremely compressed and completely enclosed in a thin bony armour which is fused with the endoskeleton; the caudal region, much abbreviated, is free and relegated to the ventral surface, the body terminating in the two dorsals, of which the first bears a strong spine. The ventral fins are far back, very small, formed of 3 or 4 rays.

_Amphisile_ is represented by three or four recent species in the Indian and Pacific Oceans, and two are known from Upper Eocene and Oligocene beds in Europe. Dr. Arthur Willey has observed these fishes in the Southern Pacific. _A. strigata_ "lives in small shoals of about half-a-dozen individuals, and swims about with rapidity in a vertical position, cleaving the water with its razor-shaped body."

FAM. 9. SOLENOSTOMIDAE.—Body moderately elongate, with large star-like ossifications. Anterior vertebrae elongate, without transverse processes; no ribs. Snout much produced, tubiform; mouth, small, terminal, toothless; no praeoperculum; symplectic elongate; gill-opening wide; gill-lamellae small rounded lobes. Two short dorsal fins, the rays of the anterior not articulated, flexible spines. Pterygials of pectoral fin very small. Ventral fins large, with 7 rays, behind the pectoral arch. No air-bladder.

The unique genus, _Solenostomus_, with three or four species from the Indian and Pacific Oceans, may be regarded as in many respects intermediate between the _Centriscidae_ and the _Syngnathidae_. In the female the inner side of the ventral fins coalesces {634}with the integuments of the body, forming a large pouch for the reception of the eggs.

_Solenorhynchus_, from the Upper Eocene of North Italy, probably belongs to this family, but its form is much more elongate, and the exoskeleton is in regular rings.

FAM. 10. SYNGNATHIDAE.—Body more or less elongate, protected by an exoskeleton forming rings. Anterior vertebrae not elongate; parapophyses strong, ankylosed to the exoskeleton; no ribs. Snout much produced, tubiform; mouth small, terminal, toothless; no praeoperculum; symplectic elongate; gill-cleft reduced to a very small opening near the upper posterior angle of the gill-cover; gill-lamellae small rounded lobes. A single dorsal fin. Pectoral fins, if present, with very small pterygials; ventrals absent. Caudal fin often absent; tail sometimes prehensile.

This family embraces about 175 marine species, and is represented over the greater part of the world. Principal genera: _Siphonostoma_, _Syngnathus_, _Penetopteryx_, _Ichthyocampus_, _Nannocampus_, _Osphyolax_, _Urocampus_, _Doryichthys_, _Coelonotus_, _Stigmatophorus_, _Nerophis_, _Protocampus_, _Gastrotoceus_, _Solenognathus_, _Hippocampus_, _Acentronura_, _Phyllopteryx_.

Remains are found in the Upper Eocene and Miocene beds of Europe, and have been referred to _Siphonostoma_ and _Syngnathus_, and to the extinct genus _Calamostoma_. It is probable that _Pseudosyngnathus_, from the Upper Eocene of Monte Bolca, is the type of a distinct family.

The best known members of this family are the Needle-Fish or Pipe-Fish (_Siphonostoma_ and _Syngnathus_) and Sea-Horse (_Hippocampus_) of our coasts. The latter, like _Amphisile_, swims with the body in a vertical position. In most species the male takes charge of the eggs, in a pouch under the tail (_Siphonostoma_, {635}_Syngnathus_, _Penetopteryx_, _Nannocampus_, _Stigmatophorus_, _Hippocampus_), in a groove under the tail (_Phyllopteryx_), or in a groove on the abdomen (_Doryichthys_, _Coelonotus_, _Nerophis_, _Gastrotoceus_).

An Australian species of _Syngnathus_ has been described by E. P. Ramsay under the name of _S. intestinalis_, from its living inside Holothurians, in the manner of _Fierasfer_, and G. Lunel has observed a _Doryichthys_ to offer a similar instance of inquilinism.

One of the most remarkable types of Syngnathids is _Phyllopteryx_, from Australia. The spines and knobs of the head and body are furnished with dermal appendages, which closely imitate the fucus among which they live.

FAM. 11. PEGASIDAE.—Body short or moderately elongate, encased in an exoskeleton forming rings. Anterior vertebrae not elongate; no ribs. Snout produced beyond the mouth, which is small, inferior, and toothless; no praeoperculum, no symplectic; gill-opening very small; gills pectinated. A single dorsal fin. Pectoral fins large, horizontal; ventrals reduced to one or two filamentous rays, behind the scapular arch. Air-bladder absent.

{636}Five or six species, referable to two genera, _Pegasus_ and _Parapegasus_, make up this family. They are very small fishes, inhabiting the coasts of China, Japan, Arabia, the Malay Archipelago, and Australia. _Pegasus_ is remarkable among all fishes in having the five anterior rays of the pectoral fin transformed into strong spines.

SUB-ORDER 8. PERCESOCES.

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

This group connects the Haplomi with the Acanthopterygii, the Scombresocidae being somewhat related to the Cyprinodonts,[706] whilst the Anabantidae show distinct affinity to the Osphromenidae in the following sub-order. Other families, previously included among the Scombriform Acanthopterygians, are placed here on the assumption that the loose attachment of the pelvic bones to the clavicles is a primitive character, and not the result of degeneration, such as occurs in some cases among true Acanthopterygians. Although this sub-order is perhaps only an artificial association, it must be borne in mind that, notwithstanding the very wide divergence which exists between the first and last families, and however dissimilar their members may appear to be at first sight, a gradual passage may be traced connecting the most aberrant types.

SYNOPSIS OF THE FAMILIES.

I. Ventral fins, if present, inserted far behind the pectorals; no spines
to the fins.

Ribs attached to the extremity of much-developed parapophyses; lower
pharyngeal bones completely united; pectoral fins inserted very
high up 1. _Scombresocidae_.

Ribs mostly sessile; lower pharyngeal bones distinct; pectoral {637}
fins nearer the ventral than the dorsal line 2. _Ammodytidae_.

II. Ventral fins, if present, more or less approximated to the pectorals.

A. Two well-developed dorsal fins, the anterior small and formed,
at least in part, of spinous rays.

1. Ribs attached to strong parapophyses.

Pelvic bones free or connected with the clavicles by ligament;
pectoral fins inserted high up 3. _Atherinidae_.

Pelvic bones suspended from the postclavicles; pectoral fins
inserted very high up; teeth very feeble or absent
4. _Mugilidae_.

Pelvic bones suspended from the postclavicles; pectoral fins
low down, with detached lower rays 5. _Polynemidae_.

Pelvic bones connected with the clavicles by ligament; pectoral
fins nearer the ventral than the dorsal line; dentition
powerful, cardiform; scales minute or absent
6. _Chiasmodontidae_.

2. Anterior ribs sessile; pelvic bones not connected with the
scapular arch; pectoral fins nearer the ventral than the
dorsal line 7. _Sphyraenidae_.

B. Spinous dorsal, if present, connected with the soft.

1. Anterior vertebrae without parapophyses; scales on head, if
present, small.

Oesophagus with lateral sacs which are beset with papillae
internally; spinous dorsal long; scales rhomboidal, in
oblique transverse series; pelvic bones free
8. _Tetragonuridae_.

Oesophagus with lateral sacs which are beset with toothed
papillae internally; spinous dorsal, if distinct, shorter
than the soft dorsal; scales moderate or small, cycloid,
often deciduous 9. _Stromateidae_.

No sacs in the oesophagus; fins without spines; scales very
small or absent 10. _Icosteidae_.

2. All, or all but the anterior two vertebrae with parapophyses;
scales on head large; a superbranchial cavity.

No spines to the fins 11. _Ophiocephalidae_.

Strong spines to the dorsal, anal, and ventral fins
12. _Anabantidae_.

FAM. 1. SCOMBRESOCIDAE.—Maxillary entering the border of the upper jaw; dentition moderately strong or feeble. Lower pharyngeal bones united. Praecaudal vertebrae with strong parapophyses supporting the ribs. Body covered with cycloid scales. Pectoral fins inserted very high up; ventral fins widely separated from the pectorals, without spines, with 6 rays. Dorsal fin opposed to the anal, and likewise formed entirely of soft rays. Air-bladder generally present, sometimes cellular.

The shape of the head and body vary greatly, and the pectoral fin may reach an extraordinary wing-like development. The dorsal fin may be followed by a series of finlets, as in many of the Scombridae. Most of the Scombresocidae, of which about 200 species are known, are marine; some are carnivorous, {638}others (_Hemirhamphus_) mainly herbivorous, feeding on green algae. Nearly all are in the habit of making great leaps out of the water, this tendency culminating in the Flying-Fish (_Exocoetus_), which skip or sail through the air in a manner the explanation of which has given rise to much controversy. According to the latest evidence[707] the sole source of motive power is the action of the strong tail while in the water; no force is acquired while the fish is in the air. The pectorals are not used as wings but as parachutes. There is every passage between the small pectoral fin of a Saurie (_Scombresox_) or a _Hemirhamphus_ and the swallow-like wings of the most developed _Exocoetus_. The genus _Hemiexocoetus_ is a very remarkable connecting form. The Gar-Pike (_Belone_), of which one species is common on our coasts, have both jaws produced into a long slender beak; the bones are green. In _Hemirhamphus_ the lower jaw only is prolonged; some of the species, living in fresh water, are viviparous, the anal fin being modified into a copulatory organ, as in many Cyprinodonts.

Scombresocidae occur in all the tropical and temperate seas. _Belone_, _Scombresox_, and _Hemirhamphus_ are found in Upper Eocene and Miocene beds of Europe, and, as stated above, _Protaulopsis_ should perhaps be referred to this family.

{639}FAM. 2. AMMODYTIDAE.—Maxillary excluded from the border of the upper jaw; mouth protractile; dentition feeble or absent. Lower pharyngeal bones separate. Praecaudal vertebrae without parapophyses. Body covered with very small cycloid scales. Pectoral fins nearer the ventral than the dorsal line; ventral fins, if present, widely separated from the pectorals, without spine, with 6 rays. Dorsal and anal fins more or less elongate, formed of soft rays. Air-bladder absent.

The existing genera, _Ammodytes_, with 8 species, from the temperate coasts of the northern hemisphere, and _Hypoptychus_, from northern Japan, with a single species, are deprived of ventral fins, and their exact relations remained obscure until the structure of the Oligocene _Cobitopsis_ revealed their affinity to the _Scombresocidae_, or at least their pertinence to the present suborder. The Greater Sand-Eel or Launce (_Ammodytes lanceolatus_) and the Lesser Sand-Eel (_A. tobianus_) are common on our coasts, and are remarkable for the manner in which, by means of their sharp-pointed snout, they bury themselves with great rapidity in the sand, darting in and out like arrows.

FAM. 3. ATHERINIDAE.—Maxillary excluded from the border of the upper jaw; dentition more or less developed. Body covered with cycloid or ctenoid scales. Ribs attached to strong parapophyses. Pectoral fins inserted high up; ventral fins more or less approximated to the pectorals, with one spine and five soft rays; pelvic bones connected with the clavicular symphysis by a ligament. Two well-separated dorsal fins, the anterior small and formed, at least in part, of spinous rays. Air-bladder present.

Carnivorous Fishes, mostly marine and of small size, much valued as food, and distributed along the coasts of most tropical and temperate seas; some inhabit fresh waters. A silvery lateral band, or "stole," is usually present. About 65 species are known, referred to 14 genera: _Atherina_, _Iso_, _Chirostoma_, _Thyrina_, _Atherinella_, _Labidesthes_, _Atherinopsis_, _Atherinops_, _Telmatherina_, _Neatherina_, _Pseudomugil_, _Rhombatractus_, _Aida_, _Melanotaenia_.

{640}Represented in the Upper Eocene of Europe by several species of _Atherina_ and by the extinct genus _Rhamphognathus_.

FAM. 4. MUGILIDAE.—Maxillary excluded from the border of the upper jaw; dentition feeble or absent. Body covered with cycloid scales. Ribs attached to the extremity of strong parapophyses. Pectoral fins inserted high up; ventral fins more or less approximated to the pectorals, with one spine and five soft rays; pelvic bones suspended from the post-clavicles. Two well-separated dorsal fins, the anterior formed of a small number of spines. Air-bladder present.

These Fishes are closely related to the preceding, of which they are a further specialisation, the pharyngeal bones having a complicated structure, much reducing the oesophageal opening, and the vertebrae being reduced in number (24 to 26 instead of 32 to 60). They feed on organic matter contained in mud, and inhabit the fresh waters and coasts of the temperate and tropical regions. The species number about 100. Principal genera: _Mugil_, _Myxus_, _Anostomus_, _Joturus_. Grey Mullets (_Mugil_) are represented on our coasts by three species, valued as food, one of which (_M. capito_) has a remarkably wide range, occurring from Scandinavia to the Cape of Good Hope. Remains referred to the same genus occur in the Miocene and Oligocene.

FAM. 5. POLYNEMIDAE.—Maxillary excluded from the border of the upper jaw; dentition feeble. Body covered with ctenoid {641}scales. Ribs attached to the extremity of strong parapophyses. Pectoral fin inserted low down, with a lower portion consisting of free rays; the upper portion, or fin proper, attached to the scapula, the lower to a fenestrate bone which appears to be formed by coalesced pterygials (Fig. 391, _pt_.). Ventral fin more or less approximated to the pectoral, with one spine and five soft rays; pelvic bones suspended from the post-clavicles. Two well-separated dorsal fins, the anterior formed of a small number of spines. Air-bladder, if present, very large.

The vertebrae number 24 (10 + 14).

Three closely allied genera: _Polynemus_, _Pentanemus_, and _Galeoides_, with about 25 species, from the shores of tropical seas, often entering rivers. Some attain a length of 4 feet, and are valued as food or for the isinglass yielded by their air-bladder. The free pectoral filaments are organs of touch, and can be moved independently of the fins.

FAM. 6. CHIASMODONTIDAE.—The deep-sea genera, _Chiasmodon_, _Pseudoscopelus_, and _Champsodon_, which have been placed either with the Gadidae, the Trachinidae, or the Berycidae, may be referred to the Percesoces, as the pelvic fins have only a ligamentous connexion with the pectoral arch. Unfortunately, the skeleton has only been examined in _Champsodon_; it is remarkably similar to that of the Atherinidae. As in _Atherinichthys_, the posterior extremity of the air-bladder is protected by a bony sheath formed by the expanded ring-like haemal processes of the anterior caudal vertebrae. Vertebrae 32 (16 + 16). The {642}scales are absent or very small and spinulose, the mouth large, with cardiform teeth; spinous dorsal short, soft dorsal and anal elongate. _Chiasmodon_ and _Pseudoscopelus_ have a complicated system of sensory organs on the body, which in the latter suggest the photophores of Scopelids. _Champsodon vorax_ is a fish of extreme voracity, swallowing prey much larger than itself. Only four species of this family are known.

FAM. 7. SPHYRAENIDAE.—Maxillary excluded from the border of the upper jaw; dentition very strong. Body covered with cycloid scales. Anterior ribs sessile, the rest inserted on parapophyses. Pectoral fin nearer the ventral than the dorsal outline; ventral fin more or less approximated to the pectoral, with 1 spine and 5 soft rays; pelvis not connected with the pectoral arch. Two well-separated dorsal fins, the anterior formed of a small number of spines. Air-bladder large. Vertebrae 24.

Carnivorous Pike-like Marine Fishes from the tropical and sub-tropical seas, often found at the mouths of rivers. The "Barracudas" form a single genus, _Sphyraena_, with about 20 species, the largest of which grow to 8 feet and are dangerous to people bathing; many are valued as food, but some are reported to be poisonous, at least at certain seasons. Remains of several species are known from the Eocene and later periods in Europe and North America.

FAM. 8. TETRAGONURIDAE.—Maxillary excluded from the border of the upper jaw; dentition feeble. Oesophagus with lateral sacs which are beset with papillae internally; a series of gill-raker-like knobs below the pseudobranchiae. Body covered with rhomboidal, striated scales in oblique transverse series, those of every single transverse series coherent. Ribs mostly sessile. Pectoral fin nearer the ventral than the dorsal outline. Ventral fin with 1 spine and 5 soft rays, near the pectoral, but pelvis free from the pectoral arch. A long continuous dorsal fin, its anterior portion formed of numerous short spines. Air-bladder absent. Vertebrae 58.

This family includes a single, rather rare fish, _Tetragonurus cuvieri_, from the Mediterranean and neighbouring parts of the Atlantic and the South Pacific. It is said to descend to great depths at certain seasons, and to feed on Medusae; its flesh is poisonous. Young specimens have been observed by Emery to live in the respiratory cavity of large Salpae.

{643}FAM. 9. STROMATEIDAE.—Although including a number of forms very unlike _Tetragonurus_ in external appearance, there is no doubt that this family, hitherto placed near the Scombridae, is very closely allied to the preceding, agreeing with it in the presence of lateral oesophageal sacs bearing internally papillae (which are besides beset with setiform teeth), and, in most genera, in the presence of a series of knobs, more or less similar to gill-rakers, below the pseudobranchiae. The pelvic bones are sometimes free from the pectoral arch, as in the Tetragonuridae, sometimes more closely attached, but only by ligament, and movable. The principal difference resides in the scales, which are always cycloid and usually very small and more or less deciduous, and in the spinous dorsal being shorter than the soft, or even quite rudimentary. The ventrals are sometimes absent. The air-bladder is present or absent. The number of vertebrae varies from 24 to 46.

Marine Fishes, pelagic or deep-sea, feeding on Crustaceans, Medusae, or the fry of other fish. About 45 species are known, referable to 10 genera: _Nomeus_, _Cubiceps_, _Psenes_, _Seriolella_, _Psenopsis_, _Centrolophus_, _Lirus_, _Stromateus_, _Peprilus_, and _Stromateoides_. Many of the species have a wide distribution, but are rare in collections.[708] The Black-Fish (_Centrolophus niger_) and its close ally _C. britannicus_, and the Rudder-Fish (_Lirus perciformis_ and _L. medusophagus_), have occurred, at rare intervals, on the British coasts. The Stromateidae were represented by several species in the Cretaceous (_Platycormus_ and _Homosoma_).

The widely distributed _Nomeus gronovii_, so remarkable for its enormous ventral fins, folding in a ventral groove, has been observed in New South Wales to be only found on the coast when the Siphonophores called "Portuguese Men-of-War" or _Physalia_ are driven ashore, the fish swimming beneath them, as the young _Caranx_ are in the habit of doing under Medusae. As observed by Waite,[709] the benefit of such a partnership must primarily be with the fish, for it is a voluntary agent, whereas the _Physalia_ has no power of locomotion. "If the fish secures safety from its enemies by entering the area embraced by the deadly tentacles of the _Physalia_, which attain a length of 10 to {644}12 feet, it must be immune to their influence: a remarkable condition, considering that small fish have often been seen in their stomachs and entangled in their tentacles." This observer adds: "It is probable that, in addition to protection, the fish derives its food from association with the _Physalia_, much as does the Remora in accompanying a shark. The _Physalia_ doubtless paralyses many more animals than it can consume—the residue falling to the lot of the fishes, which may be present to the number of ten."

FAM. 10. ICOSTEIDAE.—The so-called "Rag-Fishes," in which the skeleton is quite soft and cartilaginous, are aberrant deep-sea forms evidently related to the Stromateidae; they lack the oesophageal teeth and the processes of the last gill-arch, but _Icosteus_ at least has the gill-raker-like knobs below the pseudobranchiae. The pelvis is widely separated from the clavicles. Spines are absent in the fins, and the body is naked or covered with small cycloid scales. Vertebrae in large number (up to 70).

_Icosteus_, _Icichthys_, and _Acrotus_, each with a single species, from the Pacific coast of North America.

FAM. 11. OPHIOCEPHALIDAE.—Maxillary excluded from the border of the upper jaw. Head and body covered with cycloid scales. Anterior ribs sessile, the remainder inserted on the parapophyses. Pectoral fin low down; ventral fin, if present, near the pectoral, with 6 soft rays; pelvic bones connected with the clavicular symphysis by ligament. Dorsal and anal fins long, without spines. Air-bladder present, much elongate.

These Fishes are provided with an accessory superbranchial cavity, and are able to breathe atmospheric air. All are {645}inhabitants of fresh waters and are carnivorous. Only two genera are known: _Ophiocephalus_, with about 25 species from Eastern Asia and 3 from Tropical Africa, and _Channa_, distinguished by the absence of ventral fins, with 3 species from Ceylon and China.

FAM. 12. ANABANTIDAE.—Differ from the preceding, to which they are closely related, in having part of the dorsal and anal fins and the outer ventral ray spinous, and a shorter, Perch-like body covered with ctenoid scales. The accessory superbranchial organ is still more developed, with thin bony laminae, which are more or less folded and covered with a mucous membrane. These Fishes can live a long time out of water, and the name _Anabas scandens_, or Climbing Perch, recalls the fact that its first observers in India ascribed to it the habit of climbing up low trees by means of the spines with which its {646}gill-covers and ventral fins are armed. This species, which attains a length of 8 inches, is found in estuaries and fresh waters of India, Ceylon, Burma, and the Malay Peninsula and Archipelago; 3 other species occur in the Malay Archipelago, and 11 in Africa.

SUB-ORDER 9. ANACANTHINI.

Air-bladder without open duct. Parietal bones separated by the supraoccipital; prootic and exoccipital separated by the enlarged opisthotic. Pectoral arch suspended from the skull; no mesocoracoid arch. 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; caudal, if present, without expanded hypural, perfectly symmetrical, and supported by the neural and haemal spines of the posterior vertebrae and by basal bones similar to those supporting the dorsal and anal rays. This type of caudal fin must be regarded, as I have pointed out,[710] as secondary, the Gadidae being, no doubt, derived from Fishes like the Macruridae, in which the homocercal fin had been lost. The scapular foramen or fenestra is nearly always between the scapular and coracoid bones, as in the Trachinidae and several allied families, not in the coracoid, as in the other Acanthopterygians. The first two vertebrae have no epipleurals.

Mr. C. Tate Regan,[711] who has recently given a good definition of the Anacanthini, divides them into three families.

{647}FAM. 1. MACRURIDAE.—Mouth more or less inferior, protractile; teeth small, none on palate. Anterior vertebrae without transverse processes, with the ribs sessile, the rest with strong transverse processes supporting the ribs, which themselves bear epipleurals. Gill-membranes free from isthmus or narrowly attached; 6 or 7 branchiostegal rays; gills 3½ or 4; pseudobranchiae rudimentary or absent. Ventral fins below the pectorals, with 7 to 12 rays. Body short, tail elongate and tapering to a point, without caudal fin. A short anterior dorsal, with a single simple ray, and a long dorsal and anal meeting together at the end of the tail, formed entirely of articulated rays—the two dorsals sometimes continuous (_Lyconus_).

Deep-sea Fishes with very large eyes and small or rather large mouth, usually covered with rough spiny scales; a mental barbel is present, except in _Lyconus_, and the muciferous cavities of the skull are strongly developed, the bones being remarkably thin. About 120 species are known, some of which have a wide distribution. Macrurids have been found in all the seas where deep-sea dredging has been practised—the greatest depth at which they have been obtained being 2650 fathoms. Principal genera: _Macrurus_, _Gadomus_ (with perforate scapula) _Coryphaenoides_, _Hymenocephalus_, _Malacocephalus_, _Lionurus_, _Trachyrhynchus_, _Steindachneria_, _Bathygadus_, _Lyconus_, _Macruronus_. A larval form of this family has received the name of _Krohnius_; it is remarkable for the filamentous prolongation of the ventral rays, which recalls the larval _Trachypterus_.

FAM. 2. GADIDAE.—Mouth moderate or large, more or less protractile. Anterior vertebrae without transverse processes, with the ribs sessile, the rest with strong transverse processes, {648}usually supporting ribs,[712] which themselves bear epipleurals. Gill-membranes free from isthmus or narrowly attached; 6 to 8 branchiostegal rays; gills 4, a slit behind the fourth; no pseudobranchiae. Ventral fins jugular, with 1 to 9 soft rays. Body more or less elongate, covered with small cycloid scales. Dorsal and anal fins elongate, formed of articulated rays, sometimes divided into two or three distinct portions. Caudal fin more or less distinct, supported by the unmodified or but slightly modified neural and haemal spines of the last vertebrae, which are perfectly symmetrical (diphycercal or isocercal type).

A mental barbel is often present, as in the Macruridae, and the suture between the frontal bones has disappeared in most of the members of this very natural family. About 120 species are distinguished, mostly marine, many being adapted to life at great depths. All are carnivorous. They inhabit chiefly the northern seas, but many abyssal forms occur between the tropics and in the southern parts of the Atlantic and Pacific. Principal genera: _Gadus_, _Merluccius_, _Holargyreus_, _Lotella_, _Physiculus_, _Phycis_, _Haloporphyrus_, _Tripterophycis_, _Lota_, _Molva_, _Onus_, _Bregmaceros_, _Antimora_, _Raniceps_, _Brosmius_.

Several species, referred to _Gadus_ and _Brosmius_, have been described from the Miocene. _Nemopteryx_, which is allied to _Gadus_, is from the Oligocene.

The fishes of this family are among the most important from an economic point of view. It will suffice to allude merely by name to the following among the European forms:—The Cod-Fish (_Gadus morrhua_), the largest species, reaching a length of {649}4 feet and a weight of 100 lbs., the Haddock (_G. aeglefinus_), the Whiting (_G. merlangus_), the Bib or Pout (_G. luscus_), the Pollack (_G. pollachius_), the Coal-Fish (_G. virens_), the Hake (_Merluccius vulgaris_), and the Ling (_Molva vulgaris_). Species of _Merluccius_ occur also on the coasts of Chili and of New Zealand. The Rocklings (_Onus_ or _Motella_) are of small size; several species are of common occurrence in our tide-pools. The Burbot (_Lota vulgaris_) is a freshwater fish, exceeding a length of 3 feet, of excellent quality, but unfortunately local and rare in this country.

FAM. 3. MURAENOLEPIDIDAE.—Closely related to the Gadidae, from which they differ in not having a separate caudal fin, in the gill-openings being narrow and below the base of the pectorals, in the increased number (ten) of the pectoral pterygials,[713] and in the peculiar scales, similar to those of the Anguillidae. Ventrals with 5 rays. A mental barbel.

A single genus, _Muraenolepis_, from the coast of Kerguelen Island.

{650}CHAPTER XXIII

TELEOSTEI (_CONTINUED_): ACANTHOPTERYGII—OPISTHOMI—PEDICULATI—PLECTOGNATHI

SUB-ORDER 10. ACANTHOPTERYGII.

Air-bladder usually without open duct. Opercle well developed; supraoccipital in contact with the frontals. Pectoral arch suspended from the skull; no mesocoracoid. Ventral fins thoracic or jugular, more or less firmly attached to the clavicular arch. 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, more or less pungent, rays in the dorsal and anal fins, is by no means universal, exceptions to the rule being numerous. The mouth is usually bordered by the premaxillaries to the exclusion of the maxillaries, and if these should, by exception, enter the oral edge, they are always toothless. The ventral fins are sometimes inserted at some distance behind the base of the pectorals (_Haplodactylidae_, _Platycephalidae_), in which case, however, this is due to the elongation of the pelvic bones, which are solidly attached to the clavicular arch. The sub-order is broken up into divisions, which follow in somewhat arbitrary order, the natural affinities being opposed to a linear arrangement; the annexed diagram is intended to remedy this defect.

SYNOPSIS OF THE DIVISIONS.

I. No suborbital stay, or process extending from the suborbital bones
towards the praeoperculum; basis cranii double in the symmetrical
forms. Primary shoulder-girdle composed of a perforate scapula {651}
and a coracoid; of the four or five pterygials, or basal bones
of the pectoral fins, only one or two are in contact with the
coracoid; ventral fins thoracic.

Rays of the caudal fin not strongly forked at the base; hypural
usually with a basal spine or knob-like process on each side;
epipleural bones usually inserted on the parapophyses or on the
ribs; dorsal fin usually with strong spines; caudal peduncle
rarely much constricted I. PERCIFORMES.

Rays of the caudal fin strongly forked at the base, embracing a
considerable portion of the hypural, which always bears a basal
spine; epipleural bones usually inserted on the centra or on the
parapophyses, rarely on the ribs; dorsal spines feeble or detached;
caudal peduncle much constricted; scales usually very small or
absent II. SCOMBRIFORMES.

Rays of the caudal fin not strongly forked at the base; ventral {652}
fins with one spine and six to eight soft rays, _or_ cranium
asymmetrical III. ZEORHOMBI.

II. No suborbital stay; basis cranii double; scapula absent, the
pterygials inserted on the coracoid; ventral fins thoracic
IV. KURTIFORMES.

III. No suborbital stay; basis cranii simple; scapula and coracoid
more or less reduced, sometimes vestigial; pterygials large, only
one or two in contact with the coracoid; ventral fins thoracic
V. GOBIIFORMES.

IV. No suborbital stay; basis cranii simple; a perforate scapula;
three pterygials in contact with the coracoid; ventral fins
thoracic; a suctorial laminated disk on the upper surface of
the head VI. DISCOCEPHALI.

V. A suborbital stay, the second suborbital bone more or less produced
on the cheek or joining the praeoperculum; ventrals thoracic
VII. SCLEROPAREI.

VI. No suborbital stay; ventrals usually jugular or mental; if thoracic,
structure of the pectoral arch differing from that ascribed to the
first five divisions of this Synopsis.

Pectoral fin with vertical or subvertical base; anal fin usually
elongate, rarely small VIII. JUGULARES.

Pectoral fin with horizontal or sub-horizontal base; body exceedingly
compressed; dorsal fin with all the rays simple; anal fin absent
or very small IX. TAENIOSOMI.

DIVISION I.—PERCIFORMES.

No bony stay for the praeoperculum. Basis cranii double. Spinous dorsal usually well developed. None of the epipleural bones attached to the centra of the vertebrae in the praecaudal region. Pectoral arch with well-developed scapula and coracoid, the former pierced by a foramen or fenestra; pterygials longer than broad, more or less regularly hour-glass-shaped, four or five in number, one or two of which are in contact with the coracoid. Ventral fins thoracic.

This large group, consisting chiefly of marine forms, has members in all parts of the world, with the exception of the Arctic and Antarctic regions, and was already represented by numerous Berycidae and a few Serranidae and Scorpididae in the Upper Cretaceous. The division into families is a task of considerable difficulty, and the necessities of a linear arrangement result in the breaking up of some natural sequences. Thus it appears highly probable that the Scorpididae, themselves derived, together with the Serranidae, from the Berycidae, lead to the Carangidae in the division Scombriformes, whilst a nearly perfect passage can be traced between the Acanthuridae of this division and the Balistidae among the Plectognaths.

{653}SYNOPSIS OF THE FAMILIES.

I. Gills four, a slit behind the fourth.

A. Two nostrils on each side.

1. Ventrals with 1 spine and 6 to 13 soft rays. 1. _Berycidae_.

2. Ventrals with not more than 5 soft rays.

a. Lower pharyngeal bones not completely united, showing at least
a median suture.

α. Gill-membranes nearly always free from isthmus.

* Ventrals little if at all behind the pectorals.

† Third vertebra without transverse processes _or_ with
sessile ribs.

§ A more or less developed subocular shelf, or inner lamina
of the suborbitals supporting the eye-ball, sometimes
reduced to a mere process of the second suborbital.

‖ Ribs inserted on the transverse processes, when these
are developed.

Body covered with very large bony scales; ventrals
with a very strong spine and 2 or 3 very short
soft rays 2. _Monocentridae_.

Dorsal very short, with few graduated, adnate spines,
anal very long 3. _Pempheridae_.

Spinous dorsal usually well developed, soft dorsal
usually not much more developed than the anal;
palate usually toothed 11. _Serranidae_.

Dorsal and anal fins elongate and formed mostly of
articulated soft rays, the spines feeble and few
12. _Pseudochromididae_.

Dorsal and anal fins much elongate, without distinct
spines; body band-like 13. _Cepolidae_.

Teeth in the jaws fused to form a beak
14. _Hoplognathidae_.

Soft dorsal and anal much elongate; a separate
spinous dorsal 15. _Sillaginidae_.

Soft dorsal much longer than the anal; a separate
spinous dorsal 16. _Sciaenidae_.

‖‖ Ribs mostly sessile, behind the parapophyses; body
deep; mouth moderately large and protractile.

Post-temporal forked, distinct from skull
25. _Scorpididae_.

Post-temporal completely ankylosed to the skull;
mouth very protractile 26. _Caproidae_.

§§ No subocular shelf.

‖ Ribs mostly sessile, behind the parapophyses;
anal spines 3 to 14.

Teeth conical; palate toothed; mouth feebly
protractile 4. _Centrarchidae_.

Teeth incisor-like; fins densely scaled
5. _Cyphosidae_.

Teeth conical; palate toothless 6. _Lobotidae_.

Maxillary very slender; mouth very protractile
7. _Toxotidae_.

No entopterygoid; mouth very protractile
8. _Nandidae_.

‖‖ Ribs inserted on the transverse processes when {654}
these are developed; not more than 3 anal spines.

Mouth not or but feebly protractile; spinous dorsal
usually longer than the soft; anal with 1 or 2
spines 9. _Percidae_.

Mouth moderately protractile; palate toothed; spinous
dorsal not longer than the soft; anal with 2 or 3
spines 10. _Acropomatidae_.

Mouth very protractile; palate toothless; praemaxillary
with an upwardly directed lateral process
17. _Gerridae_.

Mouth moderately protractile; palate toothed; anal
longer than soft dorsal; body scaly
18. _Lactariidae_.

Mouth moderately protractile; palate toothless; anal
much longer than soft dorsal; body naked
19. _Trichodontidae_.

†† Transverse processes developed on the third vertebra and
bearing the ribs; palate usually toothless.

No subocular shelf; teeth small 22. _Pristipomatidae_.

A subocular shelf; teeth often large, either cutting
in front or molar-like on the sides 23. _Sparidae_.

A subocular shelf; teeth very small or absent; a pair
of barbels on the throat 24. _Mullidae_.

** Ventrals rather far behind the base of the pectorals;
lower pectoral rays unbranched, often thickened; no
subocular shelf.

Anal fin nearly as long as the soft dorsal
20. _Latrididae_.

Anal fin much shorter than the soft dorsal
21. _Haplodactylidae_.

β. Gill-membranes attached to the isthmus.

* Scales well developed; vertebrae 24 or more.

A subocular shelf; mouth small; palate toothless
27. _Chaetodontidae_.

No subocular shelf; mouth small; palate toothless
28. _Drepanidae_.

Subocular shelf more or less developed; a superbranchial
respiratory organ 31. _Osphromenidae_.

** Scales minute; mouth small; vertebrae 22 or 23.

Post-temporal not distinctly forked; vertebrae with strong
transverse processes; ventrals with 1 spine and 2 to 5
soft rays 29. _Acanthuridae_.

Post-temporal forked; vertebrae without transverse
processes; ventrals with 2 spines and 3 soft rays
between them 30. _Teuthididae_.

b. Lower pharyngeals completely united into one bone, without
median suture 32. _Embiotocidae_.

B. A single nostril on each side; lower pharyngeal bones more or
less completely united, but with persistent suture; no subocular
shelf; palate toothless 33. _Cichlidae_.

II. Gills three and a half; lower pharyngeals completely united into
one bone, without median suture; palate toothless.

A single nostril on each side; teeth conical or incisor-like;
a subocular shelf 34. _Pomacentridae_.

Two nostrils on each side; anterior teeth usually strong and
canine-like; teeth on pharyngeal bones conical or tubercular;
no subocular shelf 35. _Labridae_.

Two nostrils on each side; anterior teeth more or less coalesced
into a beak; teeth on pharyngeal bones flat, tessellated; no
subocular shelf 36. _Scaridae_.

{655}FAM. 1. BERYCIDAE.—One or several of the suborbitals emitting an internal lamina supporting the eye; entopterygoid present. 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; 4 to 10 branchiostegal rays; gills 4, a slit behind the fourth; pseudobranchiae. Lower pharyngeal bones separate. Ventral fins with 1 spine and 6 to 13 soft rays.

This family is remarkable for the retention of two archaic characters: the large number of rays to the ventral fins and the duct between the air-bladder and the digestive tract; the latter character is, however, not universal, and has only been found in two genera (_Beryx_ and _Holocentrum_). The scaling of the body varies greatly, and so does the development of the spines in the vertical fins. Several genera (_Melamphaes_, _Anoplogaster_, _Trachichthys_, etc.) have the head studded with large muciferous cavities which are covered with a thin skin. The vent is usually situated far behind the ventral fin, but in _Paratrachichthys_, a genus closely allied to _Trachichthys_, it occupies a more anterior position, between the ventrals, whilst in _Aphredoderus_ it shifts still further with age, opening on the throat in the adult.

The Berycidae were abundantly represented in Cretaceous deposits by _Beryx_ and other genera more or less closely related to living forms, and they appear to have been the precursors of other Perciform Fishes. About 70 species, referred to 13 genera, are known to live at the present day, mostly at great depths, in {656}the seas nearly all over the world. But one freshwater form is known, _Aphredoderus sayanus_, the little Pirate Perch of North America, growing to 5 inches in length. The largest marine forms (_Beryx_ and _Gephyroberyx_) measure from 1 to 2 feet.

Recent genera: _Beryx_, _Polymixia_, _Aphredoderus_, _Melamphaes_, _Plectromus_, _Scopelogadus_, _Anoplogaster_, _Caulolepis_, _Trachichthys_, _Paratrachichthys_, _Gephyroberyx_, _Myripristis_, _Holocentrum_.

Fossil genera: _Sphenocephalus_, _Acrogaster_, _Pycnosterinx_, _Hoplopteryx_, from the Upper Cretaceous. _Asineops_, from the Eocene of North America, is supposed to be allied to _Aphredoderus_. _Beryx_ is represented by several species in the Upper Cretaceous, and _Holocentrum_ occurs in the Eocene and Miocene.

FAM. 2. MONOCENTRIDAE.—The single genus _Monocentris_, with two species, one from the seas of Japan, China, and India, and one from the South Pacific, is very nearly related to the Berycidae, but differs in the absence of ribs on the anterior six vertebrae, in the very large bony scales, forming together a coat of mail, and in the structure of the ventral fin, which is reduced to a strong spine and two or three very short soft rays. The spines of the dorsal fin are very strong and isolated.