The Nematognathi.—The Nematognathi (νῆμα, thread; γνάθος, jaw), known collectively as catfishes, are recognized at once by the fact that the rudimentary and usually toothless maxillary is developed as the bony base of a long barbel or feeler. Usually other feelers are found around the head, suggesting the "smellers" of a cat. The body is never scaly, being either naked and smooth or else more or less completely mailed with bony plates which often resemble superficially those of a sturgeon. Other distinctive characters are found in the skeleton, notably the absence of the subopercle, but the peculiar development of the maxillary and its barbel with the absence of scales is always distinctive. The symplectic is usually absent, and in some the air-bladder is reduced to a rudiment inclosed in a bony capsule. In almost all cases a stout spine exists in the front of the dorsal fin and in the front of each pectoral fin. This spine, made of modified or coalescent soft rays, is often a strong weapon with serrated edges and capable of inflicting a severe wound. When the fish is alarmed, it sets this spine by a rotary motion in its socket joint. It can then be depressed only by breaking it. By a rotary motion upward and toward the body the spine is again lowered. The wounds made by this spine are often painful, but this fact is due not to a specific poison but to the irregular cut and to the slime of the spine.

In two genera, Noturus and Schilbeodes, a poison-gland exists at the base of the pectoral spine, and the wound gives a sharp pain like the sting of a hornet and almost exactly like the sting of a scorpion-fish. Most of the Nematognathi possess a fleshy or adipose fin behind the dorsal, exactly as in the salmon. In a few cases the adipose fin develops an anterior spine and occasionally supporting rays.

All the Nematognathi are carnivorous bottom feeders, devouring any prey they can swallow. Only a few enter the sea, and they occur in the greatest abundance in the Amazon region. Upward of 1200 species, arranged in 150 genera, are recorded. They vary greatly in size, from two inches to six feet in length. All are regarded as food-fishes, but the species in the sea have very tough and flavorless flesh. Some of the others are extremely delicate, with finely flavored flesh and a grateful absence of small bones.

Families of Nematognathi.—According to Dr. Eigenmann's scheme of classification,^[11] the most primitive family of Nematognathi is that of Diplomystidæ, characterized by the presence of a well-developed maxillary, as in other soft-rayed fishes. The single species, Diplomystes papillosus, is found in the waters of Chile.

Similar to the Diplomystidæ in all other respects is the great central family of Siluridæ, by far the most numerous and important of all the divisions of Nematognathi.

The Siluridæ.—This group has the skin naked or imperfectly mailed, the barbels on the head well developed, the dorsal short, inserted forward, the adipose fin without spine, and the lower pharyngeals separate. All the marine catfishes and most of the fresh-water species belong to this group, and its members, some 700 species, abound in all parts of the world where catfishes are known—"a bloodthirsty and bullying race of rangers inhabiting the river bottoms with ever a lance at rest and ready to do battle with their nearest neighbor."

The Sea Catfish.—In the tropical seas are numerous species of catfishes belonging to Tachysurus, Arius, Galeichthys, Felichthys, and other related genera. These are sleek, silvery fishes covered with smooth skin, the head usually with a coat of mail, pierced by a central fontanelle. Some of them reach a considerable size, swarming in sandy bays. None are valued as food, being always tough and coarsely flavored. Sea birds, as the pelican, which devour these catfishes are often destroyed by the sudden erection of the pectoral spines. None of these are found in Europe or in Japan. Of the very many American species the gaff-topsail catfish (Felichthys felis), noted for its very high spines, extends farthest north and is one of the very largest species. This genus has two barbels at the chin. Most others have four. The commonest sea catfish of the Carolina coast is Galeichthys milberti. In Tachysurus the teeth on the palate are rounded, in most of the others they are in villiform bands.

In most or all of the sea catfish the eggs, as large as small peas, are taken into the mouth of the male and there cared for until hatched.

The Channel Cats.—In all the rivers of North America east of the Rocky Mountains are found catfishes in great variety. The channel cats, Ictalurus, known most readily by the forked tails, are the largest in size and most valued as food. The technical character of the genus is the backward continuation of the supraoccipital, forming a bony bridge to the base of the dorsal. The great blue cat, Ictalurus furcatus, abounds throughout the large rivers of the Southern States and reaches a weight of 150 pounds or more. It is an excellent food and its firm flesh is readily cut into steaks. In the Great Lakes and northward is a very similar species, also of large size, which has been called Ictalurus lacustris. Another similar species is the willow cat, Ictalurus anguilla. The white channel-cat, Ictalurus punctatus, reaches a much smaller size and abounds on the ripples in clear swift streams of the Southwest, such as the Cumberland, the Alabama, and the Gasconade. It is a very delicate food-fish, with tender white flesh of excellent flavor.

Horned Pout.—The genus Ameiurus includes the smaller brown catfish, horned pout, or bullhead. The body is more plump and the caudal fin is usually but not always rounded. The many species are widely diffused, abounding in brooks, lakes, and ponds. Ameiurus nebulosus is the best-known species, ranging from New England to Texas, known in the East as horned pout. It has been successfully introduced into the Sacramento, where it abounds, as well as its congener, Ameiurus catus (see Fig. 229, Vol. I), the white bullhead, brought with it from the Potomac. The latter species has a broader head and concave or notched tail. All the species are good food-fishes. All are extremely tenacious of life, and all are alike valued by the urchin, for they will bite vigorously at any sort of bait. All must be handled with care, for the sharp pectoral spines make an ugly cut, a species of wound from which few boys' hands in the catfish region are often free.

In the caves about Conestoga River in Lancaster County, Pennsylvania, is a partly blind catfish, evidently derived from local species outside the cave. It has been named Gronias nigrilabris.

A few species are found in Mexico, one of them, Ictalurus meridionalis, as far south as Rio Usamacinta on the boundary of Guatemala.

Besides these, a large channel-cat of peculiar dentition, known as Istlarius balsanus, abounds in the basin of Rio Balsas. In Mexico all catfishes are known as Bagre, this species as Bagre de Rio.

The genus Leptops includes the great yellow catfish, or goujon, known at once by the projecting lower jaw. It is a mottled olive and yellow fish of repulsive exterior, and it reaches a very great size. It is, however, a good food-fish.

The Mad-toms.—The genera Noturus and Schilbeodes are composed of diminutive catfishes, having the pectoral spine armed at base, with a poison sac which renders its sting extremely painful though not dangerous. The numerous species of this genus, known as "mad-toms" and "stone cats," live among weeds in brooks and sluggish streams. Most of them rarely exceed three inches in length, and their varied colors make them attractive in the aquarium.

The Old World Catfishes.—In the catfishes of the Old World and their relatives, the adipose fin is rudimentary or wanting. The chief species found in Europe is the huge sheatfish, or wels, Silurus glanis. This, next to the sturgeon, is the largest river fish in Europe, weighing 300 to 400 pounds. It is not found in England, France, or Italy, but abounds in the Danube. It is a lazy fish, hiding in the mud and thus escaping from nets. It is very voracious, and many stories are told of the contents of its stomach. A small child swallowed whole is recorded from Thorn, and there are still more remarkable stories, but not properly vouched for. The sheatfish is brown in color, naked, sleek, and much like an American Ameiurus save that its tail is much longer and more eel-like. Another large catfish, known to the ancients, but only recently rediscovered by Agassiz and Garman, is Parasilurus aristotelis of the rivers of Greece. In China and Japan is the very similar Namazu, or Japanese catfish, Parasilurus asotus, often found in ponds and used as food. Numerous smaller related catfishes, Porcus (Bagrus), Pseudobagrus, and related genera swarm in the brooks and ponds of the Orient.

In the genus Torpedo (Malapterurus) the dorsal fin is wanting. Torpedo electricus, the electric catfish of the Nile, is a species of much interest to anatomists. The shock is like that of a Leyden jar. The structures concerned are noticed on p. 186, Vol. I. The generic name Torpedo was applied to the electric catfish before its use for the electric ray.

In South America a multitude of genera and species cluster around the genus Pimelodus. Some of them have the snout very long and spatulate. Most of them possess a very long adipose fin. The species are generally small in size and with smooth skin like the North American catfishes. Still other species in great numbers are grouped around the genus Doras. In this group the snout projects, bearing the small mouth at its end, and the lateral line is armed behind with spinous shields. All but one of the genera belong to the Amazon district, Synodontis being found in Africa.

Concerning Doras, Dr. Günther observes: "These fishes have excited attention by their habit of traveling during the dry season from a piece of water about to dry up in quest of a pond of greater capacity. These journeys are occasionally of such a length that the fish spends whole nights on the way, and the bands of scaly travelers are sometimes so large that the Indians who happen to meet them fill many baskets of the prey thus placed in their hands. The Indians suppose that the fish carry a supply of water with them, but they have no special organs and can only do so by closing the gill-openings or by retaining a little water between the plates of their bodies, as Hancock supposes. The same naturalist adds that they make regular nests, in which they cover up their eggs with care and defend them, male and female uniting in this parental duty until the eggs are hatched. The nest is constructed, at the beginning of the rainy season, of leaves and is sometimes placed in a hole scooped out of the beach."

The Sisoridæ.—The Sisoridæ are small catfishes found in swift mountain streams of northern India. In some of the genera (Pseudecheneis) in swift streams a sucking-disk formed of longitudinal plates of skin is formed on the breast. This enables these fishes to resist the force of the water. In one genus, Exostoma, plates of skin about the mouth serve the same purpose.

The Bunocephalidæ are South American catfishes with the dorsal fin undeveloped and the top of the head rough. In Platystacus (Aspredo), the eggs are carried on the belly of the female, which is provided with spongy tentacles to which the eggs are attached. After the breeding season the ventral surface becomes again smooth.

The Plotosidæ.—The Plotosidæ are naked catfishes, largely marine, found along the coasts of Asia. In these fishes the second dorsal is very long. Plotosus anguillaris, the sea catfish of Japan, is a small species striped with yellow and armed with sharp pectoral spines which render it a very disagreeable object to the fishermen. In sandy bays like that of Nagasaki it is very abundant. Allied to this is the small Asiatic family of Chacidæ.

The Chlariidæ.—The Chlariidæ are eel-like, with a soft skeleton and a peculiar accessory gill. These abound in the swamps and muddy streams of India, where some species reach a length of six feet. One species, Chlarias magur, has been brought by the Chinese to Hawaii, where it flourishes in the same waters as Ameiurus nebulosus, brought from the Potomac and by Chinese carried from San Francisco.

The Hypophthalmidæ and Pygidiidæ.—The Hypophthalmidæ have the minute air-bladder inclosed in a long bony capsule. The eyes are placed very low and the skin is smooth. The statement that this family lacks the auditory apparatus is not correct. The few species belong to northern South America.

Allied to this group is the family Pygidiidæ with a differently formed bony capsule and no adipose fin. The numerous species are all South American, mostly of mountain streams of high altitude. Some are very small. Certain species are said to flee for protection into the gill-cavity of larger catfishes. Some are reported to enter the urethra of bathers, causing severe injuries. The resemblance of certain species to the loaches, or Cobitidæ, is very striking. This similarity is due to the results of similar environment and necessarily parallel habits. The Argidæ have the capsule of the air-bladder formed in a still different fashion. The few species are very small, inhabitants of the streams of the high Andes.

The Loricariidæ.—In the family of Loricariidæ the sides and back are armed with rough bony plates. The small air-bladder is still in a bony capsule, and the mouth is small with thick fringed lips. The numerous species are all small fishes of the South American waters, bearing a strong external resemblance to Agonidæ, but wholly different in anatomy.

The Callichthyidæ.—The Callichthyidæ are also small fishes armed with a bony interlocking coat of mail. They are closely allied to the Pygidiidæ. The body is more robust than in the Callichthyidæ and the coat of mail is differently formed. The species swarm in the rivers of northern South America, where with the mailed Loricariidæ they form a conspicuous part of the fish fauna.

Fossil Catfishes.—Fossil catfishes are very few in number. Siluridæ, allied to Chlarias, Bagarius, Heterobranchus, and other fresh-water forms of India, are found in the late Tertiary rocks of Sumatra, and catfish spines exist in the Tertiary rocks of the United States. Vertebræ in the Canadian Oligocene have been referred by Cope to species of Ameiurus (A. cancellatus and A. maconnelli). Rhineastes peltatus and six other species, perhaps allied to Pimelodus, have been described by Cope from Eocene of Wyoming and Colorado. Bucklandium diluvii is found in the Eocene London clays, and several species apparently marine, referred to the neighborhood of Tachysurus or Arius, are found in Eocene rocks of England.

There is no evidence that the group of catfishes has any great antiquity, or that its members were ever so numerous and varied as at the present time. The group is evidently derived from scaly ancestors, and its peculiarities are due to specialization of certain parts and degeneration of others.

There is not the slightest reason for regarding the catfishes as direct descendants of the sturgeon or other Ganoid type. They should rather be looked upon as a degenerate and highly modified offshoot from the primitive Characins.

Order Gymnonoti.—At the end of the series of Ostariophysans we may place the Gymnonoti (γυμνός, bare; νῶτος, back). This group contains about thirty species of fishes from the rivers of South America and Central America. All are eel-like in form, though the skeleton with the shoulder-girdle suspended from the cranium is quite unlike that of a true eel. There is no dorsal fin. The vent is at the throat and the anal is excessively long. The gill-opening is small as in the eel, and as in most elongate fishes, the ventral fins are undeveloped. The body is naked or covered with small scales.

Two families are recognized, differing widely in appearance. The Electrophoridæ constitutes by itself Cope's order of Glanencheli (γλανίς, catfish; ἔγχελυς, eel). This group he regards as intermediate between the eel-like catfishes (Chlarias) and the true eels. It is naked and eel-shaped, with a short head and projecting lower jaw like that of the true eel. The single species, Electrophorus electricus, inhabits the rivers of Brazil, reaching a length of six feet, and is the most powerful of all electric fishes. Its electric organs on the tail are derived from modified muscular tissue. They are described on p. 170, Vol. I.

The Gymnotidæ are much smaller in size, with compressed scaly bodies and the mouth at the end of a long snout. The numerous species are all fishes without electric organs. Eigenmannia humboldti of the Panama region is a characteristic species. No fossil Gymnonoti are recorded.