(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.
(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.
Fig. 356.—Harmout, Clarias anguillaris (after Valenciennes). ¼ nat. size.
Cope believed an orifice at or above the axil of the pectoral fin in Noturus to be the opening of the duct of a poison-gland; "from it may frequently be drawn a solid gelatinous style ending in a tripod, each limb of which is dichotomously divided into short branches of regular length." I think this condition of things has nothing to do with a poison-organ, and is merely a repetition of what is observed in Loaches and in the Characinid Xenocharax, where I have found a gelatinous substance filling the short duct by which the membrane of the air-bladder is placed in communication with the skin and the sensory organ of the lateral line. Most Silurids can live in very foul water, taking in air from the surface, and spend a comparatively long time out of the water, without being possessed of any special apparatus for atmospheric respiration. A few genera, however, are provided with an accessory breathing organ: in Clarias, Heterobranchus, and allies, there is a dendritic superbranchial organ, in Saccobranchus a long air-sac, extending from the first branchial cleft along the side of the body, as described above, p. [295]; and these Fish can live for days on land. Clarias lazera has been observed, in Senegambia, to spend several months of the dry season in burrows, from which it emerges at night to crawl about in search of food. Many Silurids, but especially Doras and Synodontis, are known to produce sounds in and out of the water by means of a special mechanism of the air-bladder and the processes of the vertebrae above it, combined with the movements of the pectoral spine grinding in the glenoid cavity.[[672]] In South America, Doras has been observed to move rapidly on land, projecting itself forward on the pectoral spines by the elastic spring of the tail, travelling long journeys over land, from one drying pond to another, spending whole nights on the way; these migrations sometimes take place in numerous bands, baskets of the small Fish being filled by the Indians who come across them.[[673]] The African Synodontis are much in the habit of floating or swimming leisurely on the surface with the belly in the air, as was well known to the ancient Egyptians, who have frequently depicted the Fish in this anomalous position. A curious fact in connexion with this habit is that S. membranaceus and S. batensoda, in which it has most frequently been observed, show an inversion of the ordinary mode of coloration, the lower parts being dark brown or black and the upper pale silvery grey. The electric Cat-Fish (Malopterurus electricus), is also a native of Africa, occurring all over the tropical parts of that continent and also in the Lower Nile, growing to a length of three feet. Its flesh is more esteemed than that of other Silurids. It avoids light and is slow in its movements. The electrical apparatus differs absolutely from that of all other Fishes, being derived from the integument, belonging to the glandular system, and surrounding the whole body with a thick coat of grease or gelatinous substance; the apparatus is governed by a single nerve on each side proceeding from a huge ganglionic cell at the anterior extremity of the spinal cord.[[674]] The shocks given by Madopterurus are very powerful, and the Fish is called "Raad" by the Arabs, a name which means "thunder." Kept in an aquarium with other Fishes, even of the same species, the "Raad" soon kills its companions.
Fig. 357.—Synodontis decorus, from the Congo. ⅓ nat. size.