SOUTH AMERICAN NEMATOGNATHI. 383 



Form elongate, little depressed forward, the greatest 

 depth 1J in the width. Caudal peduncle broad, depressed. 

 Head rather high, its depth about equal to the length of 

 the snout; occipital roof-shaped, with two serrate ridges 

 which widen somewhat and become blunt anteriorly, 

 uniting above the posterior nares; humeral plate with a 

 low ridge which extends upward and is continued on 3 

 of the lateral plates; occipital margined by 3 nuchal 

 plates; 2 large bicarinate nuchal plates between the oc- 

 cipital and dorsal plates. 



Orbit moderate, with a broad shallow notch; the su- 

 perciliary edge coarsely hispid; orbit without the notch, 

 2J 3f in the snout, 6-7 in the head, 1-1J in the inter- 

 orbital. Snout with its margin entirely granular, pointed 

 in young, less so in adult specimens. Mouth small, the 

 lips wholly covered 'with papillae and tentacles, the 

 marginal ones largest, the lower lip emarginate; teeth 

 few, those of the upper jaw much larger than those of 

 the lower. 



Barbels well developed, longer than the diameter of 

 eye, fringed with tentacles. 



The lateral line runs close under the upper lateral keel, 

 and is composed of two pores at the posterior margin of 

 each scute. 



All the scutes in front of the dorsal carinate; the lat- 

 eral keels approximated on the 17th or 18th scute. Breast 

 and central portion of the belly backward to the vent 

 covered with small, irregular plates, the sides of the 

 belly with a series of larger plates; in the young the 

 breast is partially naked. Distance of dorsal fin from 

 tip of snout 3-3| in the length, the dorsal fin much 

 higher than long. 



Caudal short, emarginate, the upper ray produced, the 

 filament sometimes much longer than the length to its 

 base. 



