Generic characters.—Form moderately elongated, laterally compressed. Head depressed, broader than body, forming more than one-fourth of total length. Eyes small, situated far forward, and obliquely turned upward. Mouth moderate, its gape extending to the vertical of the posterior rim of orbit, but the angle of lower jaw half way to branchial aperture. Upper maxillaries extending back the same distance, thence prolonged by a cartilaginous expansion which reaches as far back as the opercular opening, and being there connected to an expansion of the skin of the lower jaw, forms a channel running back from the mouth and as long as the gape of the mouth itself. This channel is entirely free from the side of head, but only slightly movable forwards, so that it cannot serve to widen the mouth when opened.
Premaxillaries not protractile, movable at their symphysis, and only half as long as maxillaries, with which they are connected by a thin membrane, ending below orbit.
Villiform teeth on premaxillaries throughout, also on lower maxillaries to angle of mouth, and on pharyngeals; none on upper maxillaries, vomer or palate. A minute nasal aperture close behind maxillary and another opening just in front of anterior rim of orbit.
Preoperculum covered by the skin of the head.
Branchiæ four, all double, and free, opercular apertures small, as wide as base of pectorals, and separated by the whole width of the base of head.
Tongue broad and thick. Air-bladder small, liver very large and alimentary canal short.
Scales small, cycloid and thin, imbedded in the skin so as to be scarcely perceptible anterior to dorsal fin, or on back. None on ventral surface.
No lateral line perceptible. Dorsal fins two, situated far back, and rather large. Caudal small, obtusely rounded. Anal opposite to second dorsal. Ventrals united into a funnel-shaped disk opposite base of pectorals. Pectorals large and rounded. Fin rays all soft, dividing into three or four branches toward their ends. A small “papilla genitalis” in front of anal fin.
Whole fish covered with thick mucous secretion. Skin of head rather loose and soft, and perfectly smooth.