SOUTH AMERICAN NEMATOGNATHI. ' 27 



with a layer of muscle and skin, the surface of the bones 

 irregular, rugose, the interorbital portion flattish, post- 

 orbital portion with two nearly parallel median ridges. 

 Fontanel between the two median ridges, extending 

 from the occipital process to in front of the eyes, with a 

 broad bridge behind the eyes. Occipital process a deep 

 but short crest. 



Eye small, circular, 3 in snout, little more than 1 in 

 the interorbital, 3 in the interocular, 71 in the head. 



Nostrils close together, with a membrane around the 

 entire margin forming an 8-shaped figure, the portion 

 of the membrane separating the nasal openings highest. 



Maxillary barbel broad and flattened at its base^ 

 scarcely reaching the base of the pectoral. 



Snout sometimes long and pointed, usually rounded, 

 projecting considerably beyond the lower jaw. Lips 

 thick and strongly papillose. Maxillary bones reaching 

 to below the eye, 2|- in head. The anterior half of the 

 maxillary consists of a slender peduncle bearing two 

 series of teeth; the posterior portion is flattened and 

 about three times as wide as the anterior portion. In- 

 termaxillaries with a crescent shaped patch of teeth, 

 the outer four or five series compressed, incisor-like, 

 teeth of the inner series very much smaller, not incisor- 

 like. Vomer with two oval patches of large, conical 

 teeth, the patches becoming united with age. Teeth of 

 the lower jaw compressed, incisor-like, the band deep 

 in front tapering rapidly to the rictus. 



Gill membranes usually separate to below the eye, en- 

 tirely free from the isthmus. Gill-rakers 5-|-8. Pseudo- 

 branchiae well develoj)ed, not covered by a membrane. 



Skin covered with minute cirri or papillae, which are 

 especially conspicuous over the humeral region and 

 head, the tail sometimes smooth. 



Distance of dorsal fin from tip of snout 2|-2| in the 



