SOUTH AMERICAN NEMATOGNATHI. 357 



third scute behind the dorsal fin; margin of the snout with 

 finely granular plates or with more coarsely granular 

 plates, each of which has a granular swelling at its cen- 

 ter. Temporal plate with coarse, vermiculating ridges. 

 Interorbital flattish. 



Orbit 3-3J in the interorbital. Anterior half of the 

 occipital slightly tumid, the occipital sometimes with ob- 

 scure X-shaped ridges which are continued as two par- 

 allel ridges on the nuchal plates. 



Soft parts of the mouth in an oval depression; teeth 

 fine, numerous; barbels obsolete. Region between the 

 mouth and pectoral fins with marginal plates only in the 

 young, wholly covered with irregular polygonal plates in 

 the adult. 



Belly with two series of plates, each with a median 

 keel. Anal plate arrow-shaped, a small unpaired plate 

 in front of it; plate before the anal fin. elongate. Dorsal 

 plate elongate, separating one or two paired plates; six 

 or seven paired plates between the dorsal plate and the 

 occipital. Sides of the body covered with two series of 

 obscurely keeled plates which coalesce above or slightly 

 behind the anal; 20-22 paired plates between the dorsal 

 and caudal fins. 



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

 the length; dorsal fin about 3 times as high as long; the 

 first ray highest. 



Outermost caudal rays elongate, about as long as the 

 snout, or much longer than the whole head. 



Anal fin well developed, inserted under 3d or 4th dor- 

 sal ray, little lower than the dorsal fin. 



Pectoral fins short, not reaching the ventrals, ventrals 

 not to the anal fin. 



Light olivaceous, or dark brown, the rays of all the 

 fins barred; each caudal lobe with a narrow stripe of 

 dark brown, sometimes with a few flecks of light across 

 it; base of caudal sometimes with a large dusky spot. 



