SOUTH AMERICAN NEMATOGNATHI. 459 



are not able to separate the two nominal species. In 

 thoracatus there is a narrow light bar at the base of the 

 caudal, the broad black band of longijilis being more or 

 less indistinct. The breast of thoracatus is also unspot- 

 ted sometimes. 



0. pictiis is evidently equivalent to longifilis. The color 

 of exaratus is not stated. 



C. sidcatus differs in the number of fin rays. This 

 difference may be caused by the method of counting. 



C. chiquitos was based on a figure and a very poor 

 specimen. The barbels are said to be much shorter than 

 in thoracatus. 



Form rather heavy, the depth below the dorsal spine 

 little exceeding the width, becoming compressed back- 

 ward, but little lower posteriorly. Width of the head 

 equal to or shorter than its length, its depth IJ-l-J i 11 its 

 length. Ventral profile horizontal throughout, the dor- 

 sal outline of the body scarcely descending backward, 

 the profile, from the dorsal spine forward, steep; apex of 

 the first nuchal plate nearly truncate, the second ernar- 

 ginate. Foiitanel elongate in the young, becoming cir- 

 cular in the adult. Suborbital much narrower than the 

 eye in the young, broadening and covered with skin in 

 the adult; opercles hispid. 



Barbels very long, the inner ones reaching beyond 

 base of veiitrals, shorter in the very young. 



Eye small, equidistant between tip of snout and oper- 

 cular margin, or nearer the former, about 3J- in the 

 snout, 4i--5^ in the iiiterorbital. Snout somewhat 

 pointed, depressed. No teeth in the upper jaw; a small, 

 elongate group on the sides of the lower jaw. 



Width of the isthmus between the gill-openings equals 

 the length of the snout. 



Lateral laminae covering the entire sides; about four 

 pairs of them meeting on the back immediately behind 



