Pearson : Fishes of the Rio Beni Basin 13 
the upper jaw extending slightly beyond the lower; no teeth 
on vomer or palatine; teeth of the upper jaw in a band of 
equal width thruout; the lower band narrower and tapering 
backward to a point; the greater part of the eye in the an- 
terior part of the head ; maxillary barbels falling short of the 
base of the ventrals or extending almost to their middle, the 
postmentals to the base of the pectorals; the distance from 
the tip of the snout to the origin of the dorsal 3 to 3 1/5 
times in the total length ; anal fin slightly rounded ; prolonga- 
tion of the pectoral spine as long as the next ray; caudal 
deeply forked, the upper lobe considerably longer than the 
lower ; adipose fin 3.5 to 3.8 times in the total length. 
Color light to dark brown; a more or less distinct light 
longitudinal bar thru the middle of the dorsal ; the other fins 
dark and unmarked. 
Very closely related to R. foina (Muller & Troschel) but 
with much smaller eyes, narrower body, and slightly longer 
barbels. 
Pimelodus clarias (Bloch). 
17038, 9, 130-190 mm., Pena Colorado, Huachi. Sept., 1921. 
17039, 8, 100-200 mm., Rurrenabaque. Oct., 1921. 
17352, 10, 35-40 mm., Lake Rogoagua. Nov., 1921. 
Pimelodella Eigenmann & Eigenmann. 
Specimens from a given locality vary considerably in the 
nature of the serrations of the pectoral spine. Examination 
of a large series of specimens shows gradual gradations be- 
tween accepted species. 
Key to the Beni species of Pimelodella 
a. Adipose fin less than 3 in the length. 
b. Pectoral spine without thorns along the posterior border; 
maxillary barbel reaching tip of anal. 
1. buckleyi. 
bb. Pectoral spine with thorns along the posterior border. 
c. Thorns along the posterior border of the pectoral 
spine long, the longest V 2 the width of the spine, 
none coalesced; maxillary barbel reaching base 
of anal. 
2. gracilis. 
cc. Thorns along the posterior border short, the longest 
not more than % the width of the spine; an- 
terior spines coalesced; maxillary barbel reach- 
ing base of anal. 
3. roccse. 
