Pearson: Fishes of the Rio Beni Basin 
23 
peduncle rounded, its height 3% in its length; caudal fin 
deeply emarginate, the teeth ladle shaped. 
Brownish, the younger specimens from the Popoi River red- 
dish brown; pectorals, dorsal, and ventrals with dark spots 
irregularly placed on the interradial membrane; the caudal 
with fewer indistinct spots. The young without spots. 
Related to Rhinelepis asper, differing chiefly in its slender 
body. 
Pterygoplichthys multiradiatus (Hancock), Plate VI, figs. 1-4. 
17022, 2, 28 and 390 mm., Lake Rogoagua. Oct., 1921. The immature 
specimen may belong to another species. 
15353, 9, 115-310 mm., Cashiboya, Peru. W. R. Allen, Aug., 1920. 
Specimen No. 17022 agrees with the specimens from the 
Upper Amazon except for color markings. The material from 
the Upper Amazon has the supraoccipital and interorbital 
regions with 3 distinct areas from which radiating lines run 
into vermiculations. The lower surface of the head and ab- 
domen are spotted. The specimen from Lake Rogoagua has 
the supraoccipital and interorbital areas with vermiculations 
that do not run radially from these centers. The lower sur- 
face of the head and abdomen have vermiculations which are 
broken up into spots in several places. 
Regan (“Monograph of the Fishes of the Family Lorcarii- 
dse”) Trans. Zool. Soc. London, XVII, Part 3, page 229, Oct., 
1904) has described a new variety, P. multiradiatus alternans 
from Paraguay and southern Bolivia to which my specimens 
are closely related so far as color markings are concerned. 
Ancistrus megalostomus Pearson, sp. nov. Plate VII, figs. 1 
and 2. 
17007, 2 cotypes, females, 84 mm., Huachi. Aug., 1921. 
Characterized by the very wide mandibular ramus, in this 
respect resembling Cfuetostomus. 
Head 2.9; depth 6.5; D.I,7; A. 1, 4; eye 6 to 6.5; the head 
almost as broad as long; the length of the snout 1.75 times in 
the head, interorbital slightly less than 1.8 times ; mandibular 
ramus 1.1 times in the interorbital width; the snout broad and 
blunt, the naked margin wide ; the interoperculum armed with 
9 to 11 moderately strong spines; the longest is contained 6 
times in the head ; 24 scutes in a longitudinal series, 6 between 
the dorsal and the adipose spine, 11 between the anal and the 
