Fig. 264.—Malapterurus electricus.
VI. Siluridæ Proteropodes.—The rayed dorsal fin is always present and rather short; the ventrals are inserted below (very rarely in front of) the dorsal. The gill-membranes are confluent with the skin of the isthmus, the gill-opening being reduced to a short slit. Pectorals and ventrals horizontal. Vent before, or not much behind, the middle of the length of the body.
a. Hypostomatina.
Stygogenes.—Adipose fin short; dorsal and anal short; the outer fin-rays somewhat thickened and rough; palate toothless; cleft of the mouth of moderate width, with a maxillary barbel on each side; a short broad flap on each side between the nostrils, which are close together. Lower lip very broad, pendent. Eyes small, covered with transparent skin. Head covered with soft skin. Ventrals six-rayed.
These small Siluroids, which are called “Preñadillas” by the natives, together with the allied Arges, Brontes, and Astroplebus, have received some notoriety through Humboldt’s accounts, who adopted the popular belief that they live in subterranean waters within the bowels of the active volcanoes of the Andes, and are ejected with streams of mud and water during eruptions. Humboldt himself considers it very singular that they are not cooked and destroyed whilst they are vomited forth from craters or other openings. The explanation of their appearance during volcanic eruptions is, that they abound in the numerous lakes and torrents of the Andes, that they are killed by the sulphuretted gases escaping during an eruption, and swept down by the torrents of water issuing from the volcano.
Callichthys.—Adipose fin short, supported anteriorly by a short movable spine; dorsal with a feeble spine and seven or eight rays; anal short. Teeth minute or entirely absent; cleft of the mouth rather narrow, with a pair of maxillary barbels on each side, which are united at the base. Eyes small. Head covered with osseous plates; body wholly protected by two series of large imbricate shields on each side. Ventrals six-rayed.
Twelve species of this genus are known; they are small, and similarly distributed as Doras, with which they have much in common as regards their mode of life. They likewise are able to travel over land, and construct nests for their ova.
Fig. 265.—Callichthys armatus, from the Upper Amazon. Natural size.
Chætostomus.—A short adipose fin, supported anteriorly by a short, compressed, curved spine; dorsal fin of moderate length, with from eight to ten rays, the first of which is simple; anal fin short; ventral six-rayed; pectoral with a strong spine. Head and body completely cuirassed, the lower parts being sometimes naked; body rather short, with four or five longitudinal series of large imbricate scutes on each side; tail not depressed. Snout produced, obtuse in front; mouth inferior, transverse, with a single series of generally very fine bent teeth in both jaws. Interoperculum very movable and armed with erectile spines.