Chapter XXI: Appendix: To the Fishes: Palaeospondylidae—ostracodermi—heterostraci (2)

FAM. 12. CTENOTHRISSIDAE.—A curious type characterised by small praemaxillaries, large maxillaries, with feeble dentition, {560}the parietals in contact on the median line, vertebral centra without transverse processes, a moderately large dorsal with simple anterior rays, and large ventrals advanced far forwards and formed of 8 rays. Its affinities are still obscure, but the condition of the jaws decides its allocation to the suborder Malacopterygii, whilst in the position of the ventrals it is most nearly approached by the Pantodontidae. Small Fishes known only by two genera, of the Cretaceous period (England and Mount Lebanon), one with ctenoid scales (_Ctenothrissa_), the other with cycloid scales (_Aulolepis_).

FAM. 13. PHRACTOLAEMIDAE.—Mouth edentulous, projectile, bordered by the very slender praemaxillaries and maxillaries. Supraoccipital in contact with the frontals, widely separating the small parietals; operculum and suboperculum well developed; praeoperculum small; interoperculum enormous, covering the gular region and overlapping its fellow; symplectic absent. Basis cranii single. No pharyngeal teeth. Only 3 slender branchiostegal rays. Ribs stout, sessile, nearly completely encircling the body; slender epineurals; no epipleurals; caudal region very short. Supratemporal small, simple, fixed to the parietal and squamosal; no postclavicle; scapular foramen in the scapula. Pectoral fin inserted low down, folding like the ventrals; latter with 6 rays.

The remarkable little Fish, _Phractolaemus ansorgii_, discovered by Dr. W. J. Ansorge in the Niger Delta in 1900, and which has since also been found in the Congo, stands quite apart among the Malacopterygians, its nearest allies being apparently the Osteoglossidae. The body is elongate and subcylindrical, covered with large striated scales; the head is small, the skull strongly ossified, covered with thin skin; the mouth small, proboscidiform, {561}capable of being thrust forwards, when at rest folded over and received into a depression on the upper surface of the head; the narial orifice is single, and preceded by a barbel; the gill-openings are narrow, restricted to the sides. The ventral fins are inserted far back, the dorsal and anal are short. The air-bladder is very large, and the intestine extremely long and much convoluted. Vertebrae 26 + 8.

FAM. 14. SAURODONTIDAE.—Margin of the upper jaw formed by the praemaxillaries and the maxillaries, the latter the more developed and firmly united to the former; these bones, as well as the mandible, with teeth implanted in deep sockets; palate toothless. Supraoccipital separating the small parietals; opercular bones well developed; symplectic present, exposed. Basis cranii double. Ribs sessile, very low down on the centra; no parapophyses; neural arches not fused with the centra. Pectorals inserted very low down; postclavicle apparently absent. Caudal fin deeply forked, without fused hypurals.

This family, comprising several Cretaceous genera, may be regarded as ancestral to the _Chirocentridae_, with or near which it has been placed by Cope and various later authors. The normal position of the symplectic, however, entitles its members to rank as a separate family, and the autogenous neural arch, as well as the distinctness of the bones supporting the caudal fin, are also indicative of a greater generalisation. The restoration of _Ichthyodectes_ as given by Loomis, shows a general form similar to an ordinary Herring, but it does not appear to be reliable.

The members of the Saurodontidae have been referred to two groups: (_a_) with praedentary (praesymphysial) bone, _Saurocephalus_, _Saurodon_; (_b_) without praedentary, _Chirocentrites_, _Portheus_, _Ichthyodectes_, _Spathodactylus_, _Cladocyclus_. These Fishes are from the Chalk of Europe and North America, and some among them attain a very large size, perhaps not less than two metres in length.

FAM. 15. CHIROCENTRIDAE.—Margin of the upper jaw formed by the praemaxillaries and the maxillaries, the latter the more developed and firmly united to the former; these bones, as well as the mandible, with large teeth not implanted in true sockets; minute teeth on the palatines, pterygoids, and hyoid bones, Supraoccipital in contact with the frontals, separating the small parietals; opercular bones well developed; symplectic hidden {562}between the inner surface of the quadrate and a descending process of the hyomandibular. Basis cranii double. Ribs very slender, sessile, very low down on the centra; no parapophyses; epipleurals and epineurals. Pectorals inserted very low down. Post-temporal forked; postclavicle absent; a thin bony lamina, similar to the postclavicle, above the pectoral fin, attached to the scapula; scapular foramen in scapula; coracoids in contact with each other, forming a keel. Ventrals very small, with 7 rays. Brachiostegal rays 8. Air-bladder large, not communicating with the ear, incompletely divided into cells. Mucous membrane of the intestine forming a spiral fold.

The body is very elongate and strongly compressed, covered with thin, deciduous scales; the vertebrae number 75. The dorsal fin is short and opposite to the anal, which is long.

_Chirocentrus dorab_, the only representative of this family, inhabits the Indian Ocean and the seas of China and Japan.

FAM. 16. CLUPEIDAE.—Margin of the upper jaw formed by the praemaxillaries and the maxillaries. Supraoccipital separating the small parietals; opercular bones well developed. Basis cranii double. Ribs mostly sessile, inserted behind parapophyses; intermuscular bones (epineurals, epipleurals, adpleurals) usually numerous. Post-temporal forked, the upper branch attached to the epiotic, the lower to the opisthotic; post-clavicle applied to outer side of clavicle. Ventrals with 6 to 11 rays. Air-bladder large, communicating with the ear.

Four sub-families:—

(i.) THRISSOPATRINAE.—Mouth large; praemaxillaries very small; maxillaries large, with rather narrow supplemental bone, firmly attached to praemaxillaries; branchiostegals about 30; abdomen compressed to an edge, without serration; no lateral line. _Thrissopater_, from the Gault of Folkestone.

{563}(ii.) ENGRAULINAE.—Mouth moderate or large; praemaxillaries very small; maxillaries large, with narrow supplemental bones, more or less firmly attached to praemaxillaries; branchiostegals 6 to 19; abdomen rounded or more or less compressed, with or without serration; no lateral line. Recent genera: _Dussumieria_, _Etrumeus_, _Engraulis_, _Cetengraulis_, _Heterothrissa_, _Coilia_. Fossil: _Spaniodon_, Upper Cretaceous.

(iii.) CLUPEINAE.—Mouth small or moderate; maxillaries freely movable behind the praemaxillaries, usually with large supplemental bones; branchiostegals 5 to 10; abdomen usually serrated; lateral line usually absent. Recent genera: _Clupea_, _Hyperlophus_ (_Diplomystus_), _Opisthonema_, _Brevoortia_, _Pellonula_, _Clupeichthys_, _Odaxothrissa_, _Pellona_, _Chirocentrodon_, _Pristigaster_, _Raconda_, _Chatoessus_. Fossil: _Pseudoberyx_, _Histiothrissa_, _Scombroclupea_, _Leptichthys_, Upper Cretaceous.

(iv.) CHANINAE.—Mouth small, toothless; maxillaries firmly attached to praemaxillaries; branchiostegals 4, very broad; abdomen rounded or flattened; lateral line distinct. _Chanos_, recent; _Chanoides_, Upper Eocene; _Prochanos_, Cretaceous.

{564}Heralded by the genus _Thrissopater_,[647] which may be regarded as a connecting type between the Elopidae and the Clupeidae, this family is largely represented in Cretaceous times, more abundantly still in the Eocene and Miocene, where _Clupea_ and _Engraulis_ occur in numerous species; _Hyperlophus_, distinguished from _Clupea_ by the presence of a dorsal serrated ridge similar to the ventral, occurs in the Upper Cretaceous of Syria, Southern Europe, and South America, in the Eocene of North America and Europe, and is represented at the present day on the West Coast of South America and on the coast and in the rivers of New South Wales. About 200 Clupeids are known to live at the present day, mostly marine species, but a few are confined to fresh-waters; none may be termed deep-sea forms; some, like the Allis Shad (_Clupea alosa_) and Twait Shad (_C. finta_), are anadromous, ascending rivers to spawn. The range of the family is almost cosmopolitan. Several species are remarkable for the extreme abundance of individuals, as for example the Herring (_Clupea harengus_), the Pilchard or Sardine (_C. pilchardus_), and the Anchovy (_Engraulis encrasicholus_). The Herring inhabits the northern parts of the Atlantic and the seas north of Asia. As Dr. Günther first showed, the so-called "Whitebait" consists chiefly of the fry of Herrings, which, like those of the Sprat (_C. sprattus_), have a predilection for brackish water. The Anchovy and the Pilchard, on the other hand, seldom if ever enter estuaries. The eggs of the Herring, contrary to those of most British marine food-fishes, are heavy and adhesive, sticking firmly to stones or fixed objects on the sea bottom, whilst those of the Sprat and Pilchard float on the surface. The larvae are long, slender, and transparent. The Sardine, which affords so valuable a fishery on the West Coast of France, is the immature state of the Pilchard, which grows to a length of 10 to 14 inches. Its movements are not yet well understood, and its scarcity during certain years in the waters where it usually swarms has caused periodical crises in an important industry. Ripe Pilchards are mostly found at a considerable distance from the coasts. The Anchovy is especially abundant in the {565}Mediterranean, but it is also regularly fished in Holland, especially in the Zuydersee, where it breeds, as well as in the Mediterranean; it makes only temporary appearances, and has not been observed to spawn, in the English Channel, although eggs have recently been obtained off the coast of North Lancashire.[648]

The imperfectly known Cretaceous Crossognathidae (_Crossognathus_ and _Scyllaemus_), referred by some authors to the Percesoces, should probably be placed with or near the Clupeidae.

FAM. 17. SALMONIDAE.—Margin of the upper jaw formed by the praemaxillaries and the maxillaries. Supraoccipital in contact with the frontals, but frequently overlapped by the parietals, which may meet in a sagittal suture; opercular bones all well developed. Basis cranii double. Ribs sessile, parapophyses very short or absent; epineurals, sometimes also epipleurals, present. Post-temporal forked, the upper branch attached to the epiotic, the lower to the opisthotic; postclavicle, as usual, applied to inner side of clavicle. A small adipose dorsal fin. Air-bladder usually present, large. Oviducts rudimentary or absent, the ova falling into the cavity of the abdomen before exclusion.

Marine and fresh-water Fishes, mostly from the temperate and Arctic zones of the northern hemisphere: one genus (_Retropinna_) on the coasts and in the rivers of New Zealand; a few deep-sea forms (_Argentina_, _Microstoma_, _Nansenia_, _Bathylagus_) occur in the Arctic Ocean, the North Atlantic Ocean, the Mediterranean, and the Antarctic Ocean, down to 2000 fathoms. Apparently of comparatively recent age, no remains older than Miocene (_Osmerus_, _Thaumaturus_, _Prothymallus_) being certainly referable to this family. The recent genera may be grouped as follows:—

_A_. Air-bladder present.

_a_. Branchiostegal rays 8 to 20; ventral rays 9 to 13; stomach
siphonal; pyloric appendages more or less numerous (17 to 200). Breed
in fresh water. _Salmo_, _Brachymystax_, _Stenodus_, _Coregonus_,
_Phylogephyra_, _Thymallus_.

_b_. Branchiostegal rays 6; ventral rays 11 to 14; stomach caecal;
pyloric appendages in moderate numbers (12 to 20). _Argentina_.

{566}_c_. Branchiostegal rays 6 to 10; ventral rays 6 to 8; stomach
caecal; pyloric appendages few (2 to 11) or rather numerous. _Osmerus,
Thaleichthys, Mallotus, Plecoglossus, Hypomesus_.

_d_. Branchiostegal rays 3 or 4; ventral rays 8 to 10; stomach caecal;
pyloric appendages absent. _Microstoma, Nansenia, Bathylagus_.

B. Air-bladder absent; branchiostegal rays 3 to 6; ventral rays 6 or 7;
stomach siphonal; pyloric appendages absent. _Retropinna, Salanx_.

Only about 80 species can, at present, be regarded as valid.

The beauty, gameness, and great economical value of the Salmonids have caused more attention to be bestowed on them than probably upon any other group of fishes. As Professor Smitt tells us, a Swedish proverb says "A dear child has many names," and this applies well to our Salmon and Trout, the species of which have been unduly multiplied by some writers. The genus _Salmo_, characterised by a large mouth and powerful dentition, is divided into three sections: _Oncorhynchus_, Quinnat Salmon, of the North Pacific, ascending rivers in North America and Asia, with 12 to 17 developed rays in the anal; _Salmo_, Salmon and Trout, with 8 to 12 rays in the anal, and teeth not only on the head of the vomer but also along its shaft, at least in the young, {567}represented in the seas and freshwaters of Europe, Asia, and North America, extending southwards to North-West Africa, Asia Minor, Northern Persia, the Hindu Kush, the head of the Gulf of California, and the Rio Grande; _Salvelinus_, Charr, with 8 to 10 rays in the anal, and teeth on the raised head of the vomer only, of the lakes of Northern and Central Europe and the rivers of the northern parts of Asia and North America as far north as 82° 34´, sometimes descending to the sea.

The changes in form and colour which these fishes undergo when passing from fresh water into the sea or when artificially transported from one place to another are very great, and this plasticity, together with the connecting links which render the naming of not a few specimens impossible, have caused most recent students of the genus _Salmo_, in Europe at least, to reduce many of the so-called species to the rank of local varieties, and even our common Brown Trout or Brook Trout (_S. fario_) is now generally regarded as not specifically separable from the anadromous Sea Trout (_S. trutta_). The anadromous true Salmon (_S. salar_) may be distinguished by its somewhat larger scales, there being only 11 or 12 in a transverse series running from the posterior border of the adipose fin forwards to the lateral line, Trout having 13 to 16. The Charr of the lakes of Wales, the North of England, Scotland, and Ireland are also regarded as mere varieties of the common Northern migratory Charr (_S. alpinus_), of which the "Omble Chevalier" of the Swiss lakes and the "Saeblings" of the Alpine lakes of Germany and Austria are likewise varieties. An allied species (_S. fontinalis_) has been introduced into England from North America, as well as a true Trout (_S. irideus_). The large size of the eggs, their lack of {568}adhesiveness, and the fact that the ova fall into the abdominal cavity, out of which they may easily be squeezed, renders artificial impregnation particularly easy, and the species of _Salmo_ have always occupied the first place in the annals of fish-culture. Fertilised eggs are transported in ice, the development being simply suspended for several weeks, and several forms of British and American Salmonidae have thus been introduced into New Zealand and Tasmania, where some have thoroughly established themselves.

The White-Fish, _Coregonus_, are more numerous in species than _Salmo_, and as a rule more readily defined. They are easily recognised by their large silvery scales and their smaller mouth without or with minute teeth. Some, like the Houting (_C. oxyrhynchus_) of Northern Europe, occur in the sea, entering rivers to spawn, whilst others, like the Sik, Weiss, Felchen, or Lavaret (_C. lavaretus_), are confined to lakes. British species are the Gwyniad (_C. clupeoides_), of Loch Lomond, Haweswater, Ullswater, and Bala, the Vendace (_C. vandesius_), of Loch Maben, and the Pollan (_C. pollan_) of Lough Neagh in Ireland.

The Grayling (_Thymallus vulgaris_ or _vexillifer_), with its high dorsal fin formed of about 20 rays, one of the handsomest British fishes, inhabits the rivers and lakes of Northern and Central Europe, and is represented by a few allied species in Asia and North America. It derives its name from having the odour of thyme.

The Smelt (_Osmerus eperlanus_) breeds in salt water, and although it often enters rivers, it does not ascend beyond tidal influence. The Capelin (_Mallotus villosus_), of the coasts of Arctic America and North-eastern Asia, deposits its eggs in the sand along the shores in incredible numbers, the beach becoming a {569}quivering mass of eggs and sand. _Plecoglossus_, from Japan and Formosa, is highly remarkable for its lamellar, comb-like, lateral teeth. The Siel-Smelts (_Argentina_) are deep-sea Salmonids of which examples have occasionally been taken off the coasts of Scotland and Ireland; large numbers have been brought from Norway to English markets. _Bathylagus_ is still better adapted for life at great depths (down to 1700 fathoms), the eyes being of enormous size. As Dr. Günther has observed, "these fishes must be entirely dependent for vision on the phosphorescent light which is produced by other abyssal creatures. Not being fish of prey themselves, or only to a slight degree, they would be attracted by the light issuing from the Pediculates and Stomiatids of the deep, and thus form an easy prey to these fishes."

Secondary sexual characters are very strongly developed in many Salmonids. In adult males of Salmon, Trout, and Quinnat the snout becomes greatly distorted, both jaws being hooked and the base of the teeth more or less enlarged; in the latter species a fleshy hump is developed before the dorsal fin, and the scales of the back become embedded in the flesh. Pearl-like excrescences appear on the scales of many of the White-Fish during the breeding season, being more prominent in males than in females, and _Mallotus villosus_ is so called from the villous bands formed by the scales of mature males, the scales above the lateral line and along each side of the belly becoming elongate-lanceolate, densely imbricated and produced into free, projecting points.[649]

The Pachyrhizodontidae, with the Cretaceous genus _Pachyrhizodus_, are placed by some authors with the Salmonidae, but the remains at present known are too fragmentary to afford a correct idea of their exact systematic position. There seems to be less justification for placing them among the Elopidae.

FAM. 18. ALEPOCEPHALIDAE.—Deep-sea Fishes similar in general structure to the Clupeidae and Salmonidae, but destitute of a postclavicle and of an adipose dorsal fin,[650] the rayed fin being situated far back on the body, in the caudal region, and opposed {570}or slightly anterior to the anal. The skeleton of _Alepocephalus_[651] is remarkable for its feeble ossification. Epipleurals and epineurals are present, and the bilateral division of the neural arch remains perfectly distinct throughout the praecaudal region, both halves being very loosely apposed. The air-bladder is absent. Ventrals are absent in _Platytroctes_, and the snout is much produced in _Aulostomatomorpha_.

Eleven genera are distinguished:—A, with scales: _Alepocephalus_, _Conocara_, _Bathytroctes_, _Leptochilichthys_, _Narcetes_, _Platytroctes_, _Aulostomatomorpha_. B, without scales:—_Xenodermichthys_, _Aleposomus_, _Leptoderma_, _Anomalopterus_.

Represented by about 35 species in nearly all the seas; as usual with deep-sea forms, individuals of the same species have been obtained from stations very remote from one another.

FAM. 19. STOMIATIDAE.—I would unite under this name the Stomiatidae and Sternoptychidae of Günther, an assemblage of aberrant deep-sea Fishes which agree in having the maxillary bone more developed than the praemaxillary, and beset with teeth, a character which differentiates them at once from all other deep-sea forms of this sub-order, as well as from the Scopelidae among the Haplomi. The ventral fins are usually inserted very far back, and the number of their rays varies from 5 to 8. Contrary to what occurs in other groups of fishes, the pectoral fins have a tendency to reduction, and actually disappear in some genera, whilst the ventrals remain well developed; whenever the pectoral fins are fully developed, as in _Maurolicus_, _Chauliodus_, _Astronesthes_, and _Photichthys_, the mesocoracoid arch is present.[652] The form of the body varies exceedingly, even within the smaller groups into which this family has been divided; it may be excessively short and compressed, or excessively elongate, {571}but the mouth and eyes are always large, these fish being essentially predatory; the dentition is often very powerful, and may extend to the palate or be confined to the jaws. The body is naked or scaly; luminous spots (photophores) are more or less developed.[653] The development and position of the vertical fin is highly variable within this group, and the several families which have been founded upon this character have no more taxonomic importance than in the better-understood groups _Characinidae_ and _Siluridae_. All authors, besides, have been compelled to admit that the presence or absence of an adipose dorsal fin has no high significance in this case, a view which is further strengthened by Dr. Gilchrist's discovery, off the Cape of Good Hope, of a deep-sea Fish agreeing in every respect with _Astronesthes_, but for the presence of a small adipose fin, absolutely similar to the dorsal, but situated on the ventral side, immediately in front of the anus. Two species with similar ventral adipose fins have just been discovered by Dr. Brauer and referred to _Astronesthes_. I am therefore unable to adopt the elaborate arrangement in favour with the modern American school.

The genera may be arranged in five sub-families:—

I. Anal not exactly opposed to the rayed dorsal, or much longer than the
latter; no hyoid barbel.

_A_. Rayed dorsal far forward, between pectorals and ventrals;
pectorals well developed (CHAULIODONTINAE). _Chauliodus_.

_B_. Rayed dorsal above or behind the ventrals; pectorals well
developed.

1. Body more or less elongate; ventrals well developed
(GONOSTOMATINAE).

_a_. A hyoid barbel. _Astronesthes_.

_b_. No barbel. _Bathylychnus_, _Gonostoma_, _Cyclothone_,
_Triplophos_, _Photichthys_, _Bathylaco_, _Diplophos_,
_Maurolicus_, _Ichthyococcus_.

2. Body short and deep; ventrals rudimentary or absent
(STENOPTYCHINAE). _Argyropelecus_, _Sternoptyx_, _Polyipnus_.

II. Dorsal and anal opposed to each other and very far back on the caudal
region; pectorals often reduced or absent; hyoid barbel often present.
{572}(STOMIATINAE). _Stomias, Macrostomias, Echiostoma, Opostomias,
Pachystomias, Photonectes, Malacosteus, Thaumatostomias, Photostomias_.

This family, comprising about 55 species, has a world-wide distribution, but most of the known forms have been obtained from the Atlantic; some of the species occur both in the Atlantic and the Indo-Pacific. _Chauliodus_, _Astronesthes_, and _Stomias_ are among the fishes with the most formidable dentition.

FAM. 20. GONORHYNCHIDAE.—Margin of the upper jaw formed by the praemaxillaries and the maxillaries, the latter articulated above the former to the ethmoid. Supraoccipital in contact with the frontals, widely separating the small parietals; opercular bones well developed; symplectic present. Basis cranii simple. Mouth small and toothless, inferior, surrounded by thick, fringed lips. Four branchiostegal rays. Head and body entirely covered with small spiny scales. Praecaudal vertebrae with strong parapophyses, to the extremity of which slender ribs and epipleurals are attached. No postclavicle. Pectoral fins inserted low down, folding like the ventrals; latter with 10 rays.

The single existing species, _Gonorhynchus greyi_, is characterised by an elongate, cylindrical body, a pointed projecting snout bearing a single barbel, short dorsal and anal fins, the former opposed to the ventrals, and the gill-membranes broadly attached to the isthmus. Teeth are present on the pterygoid and hyoid bones. No suborbital arch. Vertebrae, 45 + 20. Air-bladder absent. Its distribution is a very wide one, the species being on record from the coasts of the Cape of Good Hope, Australia, New Zealand, and Japan.

The genus _Notogoneus_, from the freshwater Eocene beds of France and North America, has been referred to this family by Cope, and has been shown by A. S. Woodward to be closely related to _Gonorhynchus_, differing only in the absence of teeth on the palate and tongue, and in the more forward position of the dorsal fin. The genus _Charitosomus_, with several species {573}from the Upper Cretaceous of Westphalia and Mount Lebanon, has also been included in this family, but the precise shape and character of the scales have not yet been ascertained.

FAM. 21. CROMERIIDAE.—Margin of the upper jaw formed by the praemaxillaries and the maxillaries. Supraoccipital large and widely separating the very small parietals; opercular bones well developed; symplectic absent. Basis cranii simple. Mouth small and toothless, inferior; gill-opening narrow. Three branchiostegal rays. Body naked. Praecaudal vertebrae with parapophyses; ribs and epipleurals slender. No postclavicle. Pectoral fin inserted low down, folding like the ventrals.

A single genus, _Cromeria_, recently discovered in the White Nile. In its elongate, naked body and the posterior position of the dorsal fin, it resembles the Galaxiidae, to which it was at first referred. But this allocation has proved to be incorrect, now that the osteological structure of the minute Fish (only about 30 mm. long) has been worked out by Swinnerton.[654] The vertebrae number 42 to 45 (28-30 + 14-15). A long, slender air-bladder is present.

SUB-ORDER 2. OSTARIOPHYSI.

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

This is one of the most natural groups of the Class Pisces, although its members are so diversified in outward appearance as to have been widely separated in the systems of older authors. It is to Sagemehl[655] that is due the credit of having first grouped, under the above name, the Characines, the Carps, the Cat-Fishes, and the Gymnotids, the relations of which had been realised, to a certain extent, by Cope. But it was not until the homology throughout the group of the ossicula auditus, first described by E. H. Weber in 1820, had been demonstrated by Sagemehl that the justification for the course here followed appeared in its full {574}strength, as such an agreement in the structure of so complicated and specialised an apparatus can only be the result of a community of descent of the families which are possessed of it. It is invariably the anterior four vertebrae that take part in the support of the Weberian apparatus. The first vertebra is much reduced; its upper arch is absent and replaced by the ossicles termed _claustrum_ and _scaphium_[656] (the former being perhaps nothing but the modified neural arch), which fill in the space between the exoccipital and the neural arch of the second vertebra; the principal piece of the apparatus, the _tripus_, variable in form, is related to the third vertebra, of which it is regarded as a modified rib; a fibrous ligament extends from the anterior extremity of the _tripus_ to the _scaphium_, and in this ligament is inserted the fourth piece, the _intercalarium_. The various forms of this sub-order also show a complete agreement in the spinal nerves which pass through these ossicles. The parietal bones either separate the frontals from the supraoccipital or are fused with the latter.

This sub-order is divided into six families. The Characinids are the most generalised, and the others are probably derived from them in the manner expressed by the following diagram:—

_Loricariidae_ _Aspredinidae_
| |
+––––––––––––+––––––––––+
|
_Cyprinidae_ _Siluridae_ _Gymnotidae_
| | |
+–––––––––––+–––––––––––+ |
| |
+–––––––––––––––––––+–––––––––––––––––+
|
_Characinidae_.

SYNOPSIS OF THE FAMILIES

I. Parietal bones distinct from the supraoccipital; symplectic present;
ribs mostly sessile, all or the greater number of the praecaudal
vertebrae without parapophyses.

Mouth not protractile, usually toothed; pharyngeal bones normal; body
scaly; an adipose dorsal fin often present 1. _Characinidae_.

Mouth not protractile, usually toothed; pharyngeal bones normal; body
Eel-shaped, naked or scaly; vent under the head or on the throat
2. _Gymnotidae_.

Mouth usually more or less protractile, toothless; lower {575}
pharyngeal bones large, falciform; body naked or scaly; no
adipose dorsal fin 3. _Cyprinidae_.

II. Parietal bones usually fused with the supraoccipital; symplectic
absent; body naked or with bony scutes; mouth usually toothed, with
barbels; adipose fin often present.

Ribs attached to strong parapophyses; operculum well developed
4. _Siluridae_.

Ribs sessile; parapophyses absent; operculum more or less developed;
mouth inferior 5. _Loricariidae_.

Ribs sessile; strong parapophyses to the vertebrae; operculum absent
6. _Aspredinidae_.

FAM. 1. CHARACINIDAE.—Mouth non-protractile, usually bordered by the praemaxillaries and the maxillaries, rarely by the praemaxillaries only; jaws usually toothed. Parietal bones united in a sagittal suture or separated by a fontanelle; opercular bones well developed; symplectic present. Pharyngeal bones normal, with small teeth. Ribs mostly sessile; no parapophyses in the thoracic region; epipleurals and epineurals, mostly free floating. Pectoral fins inserted very low down, folding like the ventrals. Body covered with scales. An adipose dorsal fin often present.

This is a very generalised type, although perhaps not directly derived from the bony Ganoids, as believed by Sagemehl. The species number about 500, and are confined to the freshwaters of Africa and Central and South America. The classification of the family is still in an unsatisfactory state, but the division into the following groups (hardly deserving the rank of sub-families), although quite provisional, appears preferable to the highly artificial arrangement hitherto adopted:—

I. No adipose fin.

A. ERYTHRININAE.—Carnivorous; teeth strong; maxillary large;
gill-openings wide; scales cycloid. American: _Macrodon_, _Erythrinus_,
_Lebiasina_, _Pyrrhulina_, _Corynopoma_.

II. Adipose fin usually present.

B. HYDROCYONINAE.—Entirely or partially carnivorous; teeth strong;
maxillary well developed; scales cycloid; lateral line usually nearer
ventral than dorsal outline (sometimes only on the tail). African:
_Sarcodaces_, _Hydrocyon_, _Bryconaethiops_, _Alestes_, _Micralestes_,
_Petersius_. American: _Acestrorhynchus_, _Boulengerella_,
_Acestrorhamphus_, _Crenuchus_, _Chalceus_, _Brycon_, _Bryconops_,
_Bryconodon_, _Creagrutus_, _Chalcinus_, _Brachychalcinus_,
_Pseudocorynopoma_, _Stichonodon_, _Gastropelecus_, _Tetragonopterus_,
_Scissor_, _Chirodon_, _Piabucina_, _Iguanodectes_, _Aphiocharax_,
_Salminus_, _Oligosarcus_, _Agoniates_, _Paragoniates_,
_Leptagoniates_, _Anacyrtus_.

{576}C. SERRASALMONINAE.—Carnivorous; teeth strong; belly serrated;
scales cycloid. American: _Serrasalmo_, _Myletes_, _Myleus_,
_Metynnis_, _Catoprion_.

D. ICHTHYOBORINAE.—Carnivorous; teeth strong; maxillary very small;
upper jaw movable; scales ciliated. African: _Eugnathichthys_,
_Paraphago_, _Mesoborus_, _Phago_, _Ichthyoborus_, _Neoborus_.

E. XIPHOSTOMINAE.—Carnivorous; teeth very small; maxillary rather
small; scales ciliated. American: _Xiphostoma_.

F. ANOSTOMINAE.—Herbivorous, entirely or partially; teeth well
developed in both jaws; maxillary very small; gill-openings narrow;
scales cycloid. American: _Anostomus_, _Leporinus_, _Characidium_,
_Chorimycterus_, _Nanostomus_, _Nanognathus_.

G. HEMIODONTINAE.—Partially herbivorous; dentition imperfect; maxillary
well developed; scales cycloid. American: _Hemiodus_, _Caenotropis_,
_Saccodon_, _Parodon_.

H. DISTICHODONTINAE.—Entirely or partially herbivorous; teeth small but
well developed; maxillary well developed; scales ciliated. African:
_Nannaethiops_, _Neolebias_, _Distichodus_, _Nannocharax_,
_Xenocharax_.

I. CITHARININAE.—Herbivorous; teeth minute or absent; maxillary small;
scales cycloid or ciliated. African: _Citharinus_, _Citharidium_.
American: _Prochilodus_, _Curimatus_.

The genera in the above sub-families are mostly founded on the dentition and the extent of the praemaxillary and maxillary bones, which are astonishingly varied, as may be seen from the annexed figures showing the open mouths of a few of the most remarkable types. As I have already pointed out, the character often given as diagnostic of this family, viz. the maxillary forming part of the oral border, is not absolutely constant; this bone is often much reduced, and it is entirely excluded from the mouth in _Ichthyoborus_ and _Neoborus_. The branchiostegal rays {577}number 3 to 5 only. The fins never bear pungent spines, and the ventrals have 6 to 13 rays. Barbels are absent. In most of the herbivorous forms the brain-case is produced forward to the nasal capsule, whilst in most of the carnivorous forms they are separated by an interorbital septum; but there are exceptions to this correlation, and as otherwise closely related genera may differ in this respect, I have not been able to make use of the character in defining sub-families.

{578}The air-bladder is divided into an anterior and a posterior part by a constriction; the posterior part is the longer, and its anterior portion is cellular in _Erythrinus_ and _Lebiasina_. Pyloric appendages to the stomach, which are constantly absent in the Cyprinids, are more or less numerous. An accessory respiratory organ in a diverticulum above the fourth branchial arch has been observed in _Xenocharax_ and _Citharinus_.

The appearance and habits of the genera which compose this family vary greatly. Some resemble the Cyprinids and are mainly vegetarians, whilst others recall Salmonids and Pike. Among the most formidable are _Hydrocyon_, the Dogs of the Water, or Kelb-el-Bahr of the Arabs, with their powerful jaws with shark-like teeth, visible when the mouth is closed, and which grow to the size of the Salmon. The five known species inhabit the Nile and the rivers and lakes of tropical Africa. No less ferocious are the "Piranha" or "Cariba" (_Serrasalmo_) of South America, whose bite has been compared to the cut of a razor. They abound in some rivers and are much dreaded by people having to enter the water, as they fiercely bite off big pieces of flesh as with a pair of scissors, and the smell of blood is said to attract them by thousands; they show a great tenacity of life and can remain for hours out of the water. _Serrasalmo niger_ has been observed by Schomburgk to produce a grunting noise in the water. _Salminus orbignianus_, of the Plate River, "Dorado" of the Spaniards, which reaches a length of 3 feet, has the predacious habits of the Pike, and follows other fishes moving in shoals; its flesh is much valued, although very full of bones, like that of all Characinids.

{579}As an example of phytophagous types may be mentioned the Moon-Fish of the Nile (_Citharinus geoffroyi_), with its feeble dentition, deep compressed body, and falciform dorsal fin; it is often represented on the monuments of the ancient Egyptians.[657]

FAM. 2. GYMNOTIDAE.—Mouth non-protractile, bordered by the praemaxillaries and the maxillaries, the latter sometimes much reduced; jaws usually toothed. Parietal bones united in a sagittal suture, or separated by a fontanelle; opercular bones well developed; symplectic present. Pharyngeal bones normal, with small teeth. Anterior ribs sessile, the posterior inserted on transverse processes; epipleurals and epineurals. Body much elongate, Eel-like, naked or scaly; dorsal fin absent or reduced to an adipose strip; anal very long; caudal rudimentary or absent;[658] ventrals absent. Vent under the head or at a very short distance behind the throat. Gill-openings narrow.

In spite of their external appearance, these fishes have nothing to do with the Eels; they are strongly modified, degraded Characinids, as first pointed out by Reinhardt. The few genera and species (about 30) are confined to the fresh waters of Central and South America. No fossils are known. Eight genera may be distinguished:—

A. A cranial fontanelle; maxillary bone larger than the praemaxillary;
anterior nostril on the upper surface of the head; vent below the head;
body scaly: _Sternopygus_, _Eigenmannia_, _Sternarchus_,
_Rhamphosternarchus_, _Rhamphichthys_, _Steatogenys_.

B. No cranial fontanelle; maxillary bone very small; anterior nostril on
the upper lip; vent on the throat.

_a_. Body scaly: _Carapus_.

_b_. Body naked; an electric organ: _Gymnotus_.

The mouth is small or very small, and the modifications of the snout in the genera _Sternarchus_ and _Rhamphichthys_ recall those noticed among the Mormyridae. The air-bladder is divided into an anterior and a posterior part, united by a slender duct.[659] The vertebrae vary in number from 70 (_Sternopygus_) to 240 (_Gymnotus_). _Gymnotus_ is unique in this sub-order in having as many as 8 pterygials (actinosts) to the pectoral fin, as in _Anguilla_.

{580}

The best known member of this family is the so-called Electric Eel (_Gymnotus electricus_), of the Orinoco, Amazons, and intermediate river-systems. It grows to a length of 8 feet and the thickness of a man's thigh, and is much feared for the electric shocks it is able to discharge. The "Tremblador," as it is called by the Spanish-speaking inhabitants of the Orinoco district, is found only in marshes and in comparatively shallow parts of rivers, to the great annoyance of travellers who have to ford at such points, beasts of burden being frequently knocked down by the electric shock. Specimens have often been exhibited alive in this country; two brought to London in the year 1842, neither of them weighing more than one pound, had by 1848 reached the weights of 40 and 50 pounds respectively. About four-fifths of the length of the fish is occupied by the tail, which contains the electric organ; this is formed by modified muscular tissue, and consists of two huge masses, longitudinal bands or columns, of cells filled with a jelly-like substance, occupying the whole of the caudal region below the vertebral column and separated by a narrow median septum; a smaller body, of similar structure, extends along each side at the base of the anal fin. The whole apparatus is supplied with a great number of nerves branching from the spinal nerves. The electrical apparatus is exercised by the will of the fish, even to {581}a distance, but this faculty is exhausted by continuous employment, and is recovered during repose. Although apparently not exempt from exaggeration and fable, Humboldt's account in _Observations de Zoologie_, p. 497, is recommended for further information on the habits and modes of capture of _Gymnotus_.[660]

FAM. 3. CYPRINIDAE.—Mouth usually more or less protractile, toothless, bordered by the praemaxillaries and the maxillaries, or, more frequently by the praemaxillaries only. Parietal bones united in a sagittal suture, or separated by a fontanelle; opercular bones well developed; symplectic present. Lower pharyngeal bones falciform, subparallel to the branchial arches, provided with teeth arranged in one, two, or three series, and often remarkably specialised. Ribs mostly sessile; no parapophyses in the thoracic region; epipleurals and epineurals, mostly free, floating. Pectoral fins inserted very low down, folding like the ventrals. Body naked or scaly. No adipose dorsal fin.

The brain-case is produced forward to the nasal capsule. The branchiostegal rays are reduced to 3; the branchiostegal membrane is usually more or less extensively grown to the isthmus. The suborbital branch of the sensory canals is usually produced on the operculum, as in the Characinidae. The ventral rays number 7 to 12, rarely 5 or 6. Pyloric appendages to the stomach are absent.

Freshwater fishes feeding on vegetable substances or small animals, and dispersed over the whole world with the exception of South America, Madagascar, Papuasia, and Australasia. The species are exceedingly numerous, about 1300 being known, referable to four sub-families, as proposed by Sagemehl.

(i.) CATOSTOMINAE.—Margin of upper jaw formed in the middle by the small praemaxillaries and on the sides by the maxillaries, which are hidden in thick fleshy lips; no barbels; pharyngeal teeth in a single row, very numerous, comb-like; air-bladder large, divided into two or three parts by transverse constrictions, not surrounded by a bony capsule. Mostly from North America; two species from China and one from Eastern Siberia. Fossil in the Lower Tertiary of North America.

Principal genera:—_Sclerognathus_, _Carpiodes_, _Catostomus_, _Moxostoma_.

{582}(ii.) CYPRININAE.—Maxillaries not bordering the mouth; barbels absent, or one or two pairs; pharyngeal teeth in one to three rows, in small number, often very large, and working against a sclerous plate attached to a ventral process of the basi-occipital, which extends under the anterior vertebrae. Air-bladder usually large and divided into an anterior and a posterior part, rarely tripartite, not surrounded by a bony capsule. The great bulk of the family, represented in every part of its range. Remains of several of the existing genera have been found in Oligocene and later beds of Europe, Sumatra, and North America.

Principal genera:—_Cyprinus_, _Catla_, _Catlocarpio_, _Osteochilus_, _Labeo_, _Discognathus_, _Psilorhynchus_, _Capoëta_, _Barbus_, _Gobio_, _Pseudogobio_, _Saurogobio_, _Rhinogobio_, _Oreinus_, _Schizothorax_, _Ptychobarbus_, _Gymnocypris_, _Diptychus_, _Aulopyge_, _Ceratichthys_, _Pimephales_, _Campostoma_, _Cochlognathus_, _Exoglossum_, _Meda_, _Lepidomeda_, _Rhinichthys_, _Rohteichthys_, _Leptobarbus_, _Rasbora_, _Luciosoma_, _Nuria_, _Amblypharyngodon_, _Cyprinion_, _Semiplotus_, _Xenocypris_, _Leuciscus_, _Tinca_, _Leucosomus_, _Chondrostoma_, _Achilognathus_, _Rhodeus_, _Danio_, _Pteropsarion_, _Hypophthalmichthys_, _Abramis_, _Nematabramis_, _Aspius_, _Leucaspius_, _Alburnus_, _Barilius_, _Bola_, _Neobola_, _Chelaethiops_, _Chela_, _Culter_, _Pelecus_, _Parapelecus_, _Cachius_, _Opsariichthys_, _Scombrocypris_, _Squaliobarbus_, _Luciobrama_.

(iii.) COBITIDINAE.—Maxillaries not bordering the mouth; barbels three to six pairs; pharyngeal teeth in one row, in moderate number. Anterior part of the air-bladder divided into a right and left chamber separated by a constriction, and enclosed in a bony capsule, the posterior part free, or absent. Loaches, characterised externally by a low, elongate body, without or with minute scales. Europe, Asia, Abyssinia. Miocene of Oeningen.

Principal genera:—_Botia_, _Lefua_, _Diplophysa_, _Nemachilus_, _Misgurnus_, _Cobitis_, _Lepidocephalichthys_, _Acanthophthalmus_, _Eucirrhichthys_, _Apua_.

(iv.) HOMALOPTERINAE.—Maxillaries not bordering the mouth, which is inferior; barbels three or four pairs; pharyngeal teeth in one row, in moderate number. Air-bladder rudimentary, divided into two lateral halves, encased in a bony capsule. Mountain forms with depressed head and horizontally expanded paired fins. China, India, Further India, Malay Peninsula and Archipelago.

Genera:—_Homaloptera_, _Helgia_, _Glaniopsis_, _Gastromyzon_.

The recently described _Gyrinochilus_, from Borneo, resembling {583}_Homaloptera_ in habit, with two gill-clefts on each side, an upper and a lower, a tadpole-like mouth without barbels, and a small, free air-bladder, should probably be regarded as the type of a fifth sub-family.

Many of the genera of the Cyprininae are partly founded on the shape and the disposition of the pharyngeal teeth, which, adapted to various requirements, may be conical, hooked, spoon-shaped, molariform, etc., etc. The importance attached to the disposition of these teeth in one, two, or three series for the definition of genera, has been rather exaggerated.[661]

The Cyprinids constitute the majority of the freshwater fishes in Europe, Asia, and North America; they are comparatively few (about 100 species) in Africa, where they coexist with the Characinids. Some, like the Carp (_Cyprinus carpio_) and the Tench (_Tinca vulgaris_), are sluggish, except during the breeding season, when they show great excitement and indulge in leaps out of the water; others, like the Bleak (_Alburnus lucidus_) are constantly on the move in large shoals near the surface; whilst others again, like the M‘Biriki of Lake Tanganyika (_Barbus tropidolepis_), behave after the manner of Salmon and Trout, {584}travelling long distances, against rapids and over waterfalls, to reach their breeding places at the heads of rivers. During the breeding season, the males of many species assume a more brilliant livery, or develop pearl-like or spiny excrescences on various parts of the head, or also on the body and fins.[662] Cyprinids are oviparous, with the exception of a small Barbel from Natal, discovered and described by Prof. Max Weber as _Barbus viviparus_.

A most striking instance of symbiosis is offered by a little Carp-like fish of Central Europe, the "Bitterling" (_Rhodeus amarus_). The genital papilla of the female acquires a great development during the breeding season, becoming produced into a tube nearly as long as the fish itself; by means of this ovipositor the comparatively few and remarkably large eggs, measuring 3 millimetres in diameter—the fish being only 60 to 80 millimetres long—are introduced through the gaping valves, between the branchial laminae of pond mussels (_Unio_ and _Anodonta_) where, after being inseminated, they undergo their development, the fry leaving their host about a month later, having attained a length of 10 or 11 millimetres.[663] The mollusc reciprocates by throwing off its embryos on the parent fish, in the skin of which they remain encysted for some time, the period of reproduction of the fish and mussel coinciding.

Some members of this family grow to a very large size,—4 to 6 feet; such is the case with the Carp, a native of Asia, introduced into England towards the beginning of the seventeenth century; the Catla (_Catla buchanani_) of India, Burma, and Siam; the Mahaseer (_Barbus mosal_) of the mountain streams of Asia, the scales of which may be as large as the palm of a hand; and _Hypophthalmichthys molitrix_ of China and Manchuria, remarkable for the low position of the eyes, the fusion of the gill-rakers into thin plates of spongious appearance, which must act as a most efficient sifting apparatus, and the presence of an involuted problematic superbranchial organ to each branchial arch.[664]

Among well-known aberrations produced by artificial selection may be mentioned the "Leather Carp," a race in which the scales are either lost or much reduced in number, and enlarged {585}along the lateral line and the back, and the Gold-Fish, a variety of _Cyprinus carassius_, remarkable for its golden or bright red colour, or its perfect albinism, as well as its monstrous form the Telescope Fish, with enormously projecting eyes, and enlarged, horizontally spread caudal fin.[665] This family has also yielded numerous more or less well-established examples of hybridism, congeneric and digeneric, originally described as distinct species, the produce of which is believed to be in some cases fertile for at least one generation.

The crystalline silvery colouring matter of various Cyprinids is said to have been employed from time immemorial for ornamental purposes by the Chinese. The well-known and important industry of "Essence Orientale" and artificial pearls, carried on in France and Germany with the scales of the Bleak, was not introduced before the middle of the seventeenth century.

The Loaches, Cobitidinae, which form a very natural sub-family, are small fishes, few species growing to a foot in length, mostly living in small streams and ponds. Many delight in the mud at the bottom, in which they move like Eels. In some cases, the branchial respiration appears to be insufficient, and the intestinal tract acts as an accessory breathing organ. The air-bladder, which is partially encased in a bony capsule, may be so reduced as to lose its hydrostatic functions and becomes transformed into a sensory organ, its outer exposed surface being connected with the skin by a meatus between the bands of muscle, and conveying the thermo-barometrical impressions to the auditory nerves; hence the name of "Wetterfisch," by which Loaches are known in some parts of Germany.

The Homalopterinae are more or less perfectly adapted to life in rapid streams, the most remarkable in this respect being {586}_Gastromyzon_ of North Borneo, in which the pectoral and ventral fins are much expanded to form, with the belly, a sucker by which the fish adhere to the stones of mountain torrents, showing a remarkable analogy to _Exostoma_ among the Silurids.[666]

FAM. 4. SILURIDAE.—Mouth non-protractile, bordered by the praemaxillaries and the maxillaries, or by the praemaxillaries only, the maxillaries being often rudimentary and supporting the base of a barbel; jaws usually toothed. Parietal bones usually confluent with the supraoccipital, forming a single large plate (parieto-occipital); symplectic and suboperculum absent. Pharyngeal bones normal, with small teeth. Ribs attached to the lower surface of long parapophyses; epipleurals absent. Pectoral fins inserted very low down, folding like the ventrals, often armed, like the dorsal, with a strong bony spine. Body naked or with bony plates. An adipose dorsal fin often present. One to four pairs of barbels.

The skull and the opercular apparatus show a reduction in the number of elements as compared with the Characinids and Cyprinids, such as the absence of the metapterygoid, the often rudimentary, rod-like condition of the palatine, and the fusion of the parietals with the supraoccipital.[667] The scapular arch is solidly united to the skull and is often very massive, and the occiput may be connected with the base of the dorsal fin by a buckler formed by the expansion of the first and second inter-neural bones. The pterygials or supports of the pectoral rays are large and reduced to two or three.[668] Teeth are rarely present {587}on the maxillary bones (_Diplomystes_, _Eutropiichthys_), being usually confined to the praemaxillaries and dentaries; they often occur on the palate. The branchiostegal rays vary from 4 to 17. The lips are sometimes much developed, and may form a sucking disk, as in _Euchilichthys_ and _Exostoma_. As in the Cyprinids, the pungent spines which may arm the fins have nothing in common with the true spines of Acanthopterygians; they result from the co-ossification, with age, of successive articles; but, contrary to the condition in the Cyprinids, the axis of the spine is single, not double. The ventral rays vary from 6 to 16, 6 being the most frequent number. Some of the exterior vertebrae may be solidly fused together, and also with the occipito-nuchal buckler. Prof. Ramsay Wright[669] has shown, by a study of the development, that the complex which follows the first vertebra, which is more or less rudimentary, if distinct, represents the fusion of the 2nd, 3rd, and 4th vertebrae, without even nerve-foramina denoting its compound origin; the first, strongly developed, transverse process represents that of the 4th vertebra. The air-bladder is usually large and trilocular, but additional septa may greatly complicate its structure, and external diverticula may also exist;[670] it may be more or less reduced and entirely or partially enclosed in a bilateral bony capsule formed by the transverse processes of the vertebrae, and sometimes (_Nematogenys_) ankylosed to the skull. In a few genera, like _Cetopsis_, the air-bladder seems to be altogether absent: it is reduced to two small oval sacs encased in the large compound anterior vertebra. As in Loaches, the air-bladder is often in immediate contact with the skin behind the shoulder-girdle. The intestinal tract may be simple and short (carnivorous forms) or extremely long and convoluted (_Callichthys_); as in Cyprinids, pyloric appendages are absent.

Cat-Fishes, as Silurids are usually called, are a large family embracing some 1000 species, spread over the fresh waters of all parts of the world, but mostly from between the tropics.[671] Only a few are marine (_Plotosus_, _Arius_, _Galeichthys_).

This family may be divided into eight subfamilies

{588}(i.) CLARIINAE.—Dorsal and anal fins very long, extending to the caudal; gill-membranes free, or narrowly united to the isthmus. Asiatic-African genera: _Clarias_, _Heterobranchus_, _Plotosus_. Asiatic-Australian: _Copidoglanis_. Asiatic: _Cranoglanis_. African: _Clariallabes_, _Allabenchelys_, _Gymnallabes_, _Channalabes_. Australian: _Cnidoglanis_.

(ii.) SILURINAE.—Dorsal fin very short or absent, anal very long; gill-membranes free. Europaeo-Asiatic: _Silurus_. Asiatic: _Silurodon_, _Silurichthys_, _Saccobranchus_, _Wallago_, _Belodontichthys_, _Cryptopterus_, _Callichrous_, _Hemisilurus_, _Ailiichthys_, _Ailia_, _Schilbichthys_, _Laïs_, _Pseudeutropius_, _Pangasius_, _Osteogeniosus_, _Helicophagus_, _Silondia_. African: _Eutropius_, _Schilbe_, _Siluranodon_, _Physailia_, _Parailia_. Australian: _Eumeda_, _Neosilurus_.

(iii.) BAGRINAE.—Dorsal fin short, followed by a more or less elongate adipose fin; anal short or moderate; gill-membranes free. Asia, Africa, America, Australia: _Arius_. Asia and America: _Amiurus_. Asiatic: _Macrones_, _Pseudobagrus_, _Liocassis_, _Bagroides_, _Bagrichthys_, _Rita_, _Acrochordonichthys_, _Acysis_, _Olyra_, _Hemipimelodus_. African: _Bagrus_, _Clarotes_, _Chrysichthys_, _Gephyroglanis_, _Auchenoglanis_, _Notoglanidium_, _Anoplopterus_, _Galeichthys_. American: _Diplomystes_, _Paradiplomystes_, _Aelurichthys_, _Genidens_, _Noturus_, _Callophysus_, _Pimelodus_, _Pimelodina_, _Nanoglanis_, _Heptapterus_, _Nematogenys_, _Pariolius_, _Pirinampus_, _Conorhynchus_, _Notoglanis_, _Callophysus_, _Sorubim_, _Piramutana_, _Bagropsis_, _Sciades_. Australian: _Nedystoma_, _Pachyula_.

(iv.) DORADINAE.—A short-rayed dorsal fin and an adipose, the latter sometimes replaced by a second rayed dorsal; anal short or moderate; gill-clefts more or less widely interrupted below. African: _Synodontis_, _Chiloglanis_, _Atopochilus_, _Euchilichthys_, _Mochocus_, _Doumea_, _Phractura_, _Paraphractura_, _Andersonia_, _Trachyglanis_, _Belonoglanis_. Asiatic: _Bagarius_, _Glyptosternum_, _Gagata_, _Pseudecheneis_, _Exostoma_, _Sisor_, _Breitensteinia_, _Sosia_, _Chaca_. South American: _Doras_, _Oxydoras_, _Leptodoras_, _Physopyxis_, _Glanidium_, _Centromochlus_, _Wertheimeria_, _Cetopsis_.

(v.) MALOPTERURINAE.—No rayed dorsal fin, an adipose; anal short; gill-clefts interrupted below. African: _Malopterurus_.

(vi.) CALLICHTHYINAE.—Dorsal, anal, and adipose fins short; body completely cuirassed; praemaxillaries much reduced, the border of the upper jaw formed mainly by the maxillaries. South American: _Callichthys_, _Corydoras_.

{589}(vii.) HYPOPHTHALMINAE.—Dorsal fin short, behind the ventrals, anal long; gill-clefts wide or interrupted below. South American: _Ageniosus_, _Trachelyopterus_, _Auchenipterus_, _Epapterus_, _Tetranematichthys_, _Hypophthalmus_, _Helogenes_.

(viii.) TRICHOMYCTERINAE.—Dorsal fin short, far back, behind the ventrals; no adipose fin; anal short; operculum and interoperculum armed with erectile spines. South American: _Trichomycterus_, _Eremophilus_, _Stegophilus_, _Vandellia_, _Acanthopoma_.

Our knowledge of the distribution in time of the Silurids is still very scanty, and throws no light on the derivation of the group. _Arius_, and two genera apparently related to it, _Rhineaster_ and _Bucklandium_, have left remains in the Eocene of Europe and North America, and traces of various recent genera have been found in later Tertiary deposits in Europe, Asia, and North and South America.

The habits of the Silurids are extremely diversified, and the shape of the body varies accordingly. The body may be very short and the head enormous and excessively depressed, for instance in the Indo-Burmese _Chaca lophioides_, which, as its name implies, resembles the Fishing-Frog or Angler; stout and _Cottus_-like in some South American _Pimelodus_; Loach-like in _Trichomycterus_ and _Stegophilus_; more or less Eel-shaped in _Clarias_ and its allies, etc.; the extreme of slenderness obtains in the African _Channalabes_, the body being excessively elongate (over 100 vertebrae), the ventral fins absent, and the pectorals rudimentary or absent. Among other remarkable forms may be mentioned the Indian _Sisor_, which resembles _Aspredo_, and in which the upper caudal ray is much thickened and greatly prolonged; _Pseudecheneis_, living in rapids of the Himalayas and Khasia hills, provided with a transversely plaited ventral disk between the pectoral fins; the African _Phractura_ and _Andersonia_, resembling _Loricaria_; and the likewise African _Belonoglanis_, comparable to a Needle-Fish. The spines which so frequently arm the dorsal and pectoral fins may be barbed or serrated, and constitute formidable defensive weapons; in the South American _Ageniosus valenciennesi_, the maxillary bone is transformed into a strong, barbed, erectile spine, replacing the barbel. Stings of even the smaller Cat-Fish are at least as painful as that of a bee, and this is probably due to some poisonous property of the dermal secretion of the Fish.

{590}