42 
Indiana University Studies 
dorsal area narrowly rounded ; 15 scales between the occipital 
process and the origin of the dorsal; dorsal truncate, the 
highest ray .85 the length of the head, its origin much nearer 
the tip of the snout than the base of the caudal, separated from 
the adipose by 6 or 7 scales when depressed; preventral area 
rounded ; the pectorals usually not quite reaching the base of 
the ventrals ; ventrals almost reaching anal, occasionally 
reaching the anal ; anal emarginate ; scales of the lower caudal 
lobe adherent, no pouch in the males. 
An oval spot just above the lateral line, covering scales 3 
to 5; caudal spot large, extending to the end of the middle 
caudal rays ; a wide, rather indistinct, lateral band ; chromato- 
phores collected into spots at the bases of the caudal scales. 
Hemibrycon huambonicus (Steindachner) . 
17318, 7, 42-88 mm., Rio Colorado, Lower Bopi. Sept., 1921. 
17319, 20, 48-98 mm., Popoi River, Upper Beni. Sept., 1921. 
17320, 30, 28-57 mm., Tumupasa. Dec., 1921. 
Hemibrycon beni Pearson, sp. nov. Plate II, fig. 6. 
17321, 48 cotypes, 25-68 mm., in good condition, 58, 33-95 mm. dried 
during shipment, Espia. July, 1921. 
17347, 6, 26-30 mm., Rio Colorado, Lower Bopi. Sept., 1921. 
Head 3% to 4; depth 3 to 3 1/3; D.10; A. 21 or 22; eye 
2 2/3 to 3 times in the head; lateral line 6 or 7 — 42 to 46 — 5 ; 
about 11 strong teeth along almost the entire edge of the 
maxillary, gradually decreasing in size outward; 4 or 5 teeth 
in the outer series of the premaxillary, 4 in the inner ; mandible 
with 4 large teeth in front, the third the largest, followed 
abruptly by about 8 smaller teeth; second suborbital in con- 
tact with the preopercle below, a narrow naked area posterior ; 
10 gill rakers on the lower gill arch, their length % that of 
the gill filament ; parietal fontanel twice as long as the frontal ; 
dorsal and ventral profiles equally convex ; predorsal area nar- 
rowly rounded, 18 scales in a median series; origin of dorsal 
equidistant from the tip of the snout and the base of the 
caudal, its margin rounded; preventral region rounded, with 
a median series of 16 scales ; pectorals scarcely reaching ven- 
trals; ventrals reaching anal opening; anal rounded, the 
longest ray not reaching tip of last ray when depressed; the 
scales thin, paper-like, not rigid; the base of the caudal 
usually with a large abnormal scale above and below the 
