This genus, with the allied Plecostomus, Liposarcus, Pterygoplichthys, Rhinelepis, Acanthicus, and Xenomystus, is well represented in the fresh waters of South America, whence about sixty species are known. The majority do not exceed a length of twelve inches, but some attain to more than double that size. In some of the species the male is provided with long bristles round the margin of the snout and interoperculum.
Fig. 266.—Upper and Lower side of the head of Chætostomus heteracanthus, Upper Amazons.
Hypoptopoma.—Differing from Chætostomus in the peculiar formation of the head, which is depressed, spatulate, the eyes being on the lateral edge of the head. The movable gill-covers are reduced to two bones, neither of which is armed, viz.—the operculum small and placed as in Chætostomus, and a second, larger one, separated from the eye by the narrow sub-orbital ring, and placed at the lower side of the head.
Fig. 267.—Hypoptopoma thoracatum, Upper Amazons. Natural size.
Loricaria.—One short dorsal fin; anal short; the outer ray of each fin thickened, but flexible. Head depressed, with the snout more or less produced and spatulate. Mouth situated at the lower side of the snout, remote from its extremity, transverse, surrounded by broad labial folds which are sometimes fringed; a short barbel at each corner of the mouth. Teeth in the jaws small, bent, with a dilated, notched apex, in a single series, sometimes absent. Head and body cuirassed; tail depressed, long; eye rather small or of moderate size.
Fig. 268.—Loricaria lanceolate, Upper Amazons. Natural size.
Small fishes from rivers of tropical America; about twenty-six species are known. The male of some species has a bearded or bristly snout.