Pearson: Fishes of the Rio Beni Basin 
45 
Creagrutus beni Eigenmann. 
17310, 64, 38-75 mm., Tumupasa. Dec., 1921. 
17311, 55, 30-83 mm., Popoi River, Upper Beni. Sept., 1921. 
17312, 31, 34-82 mm., Rio Colorado, Lower Bopi. Sept., 1921. 
17313, 29, 33-83 mm., Rio Iniqui, Upper Beni. Sept., 1921. 
17314, 1, 58 mm., Rurrenabaque. Sept., 1921. 
17315, 2, 44 and 51 mm., Ixiamas. Dec., 1921. 
17316, 2, 62 and 64 mm., Huachi. Aug., 1921. 
Piabina beni Pearson, sp. nov. Plate X, fig. 5. 
17317, 11, 30-40 mm., Popoi River, Upper Beni. Sept., 1921. 
Very closely related to P. argentea from which it differs by 
having the premaxillary bones more angular, thus leaving a 
greater space between the first and third rows of teeth. 
Head about 4; depth 3; D.10 ; A. 20 to 23; lateral line 5-37 
to 39-4; eye about 2*4; second suborbital leaving a rather 
wide naked area behind and below; parietal fontanel 1% 
times as long as the frontal ; interorbital slightly less than 
the diameter of the eye; maxillary with 2 teeth, its length 
equal to 7/10 the diameter of the eye; 5 teeth in the front 
series of the premaxillary, the third slightly withdrawn, the 
fourth entirely so ; posterior row of 4 teeth, a single tooth 
between the anterior and posterior rows that has apparently 
withdrawn from the anterior row; mandible with 2 large 
teeth in front, followed by 4 teeth on the sides which regu- 
larly decrease in size; 7 gill rakers on the lower gill arch, 
their length equal to about 1 /3 that of the gill filament ; dorsal- 
profile more strongly arched than the ventral ; predorsal area 
rounded, with a median series of 14 scales ; origin of the 
dorsal nearer to the tip of the snout than to the base of the 
caudal, the second ray the longest, extending beyond the last 
ray when depressed; preventral area rounded, with a median 
series of 12 scales; origin of the ventrals slightly in advance 
of the origin of the dorsal ; origin of the anal slightly posterior 
to the last dorsal ray; pectorals just reaching the base of the 
ventrals ; ventrals reaching anal. 
A vertical humeral spot, mostly above the lateral line; a 
silvery lateral band ; an indistinct caudal spot. 
