378 FISHES OF WESTERN SOUTH AMERICA 
They differ in the depth; the verticality of mouth and chin; the greater size of the 
eye in jussiev; the extension of the enameled bucklers to enclose nearly all the 
anterior half of the fish. Our specimens more consistently dark than the dark 
carache negro. 
Dorsal profile strongly and evenly arched from the eye to the end of the dorsal 
basis, thence slightly concave; ventral profile only perceptibly convex to the origin 
of the anal fin, whose base forms a reéntrant angle with the straight, elongate caudal 
peduncle. The box-like form of the forward parts, with the rudder-like caudal 
apparatus is reminiscent of some of the trunk- or box-fishes. The greatest depth 
in the vertical through the pectoral base, nearly equal to the length of the head in 
the smaller specimens, exceeding that measurement in the good-sized ones, 2.7—3.5 
in the length. Little expanded at the shoulder, contours rounded, width 1.2—1.4 
in the head, 4.2—4.6 in the length. Caudal peduncle short, but narrow, its depth 
equal to the postorbital portion of the short head. 
Head rather short, although but 3.3-3.7 in the moderate length; crown convex 
in cross section, slightly to considerably depressed before the eye; snout narrow, 
rather pointed; chin deep, truncate, vertical, mandible equal to interorbital space; 
mouth vertical, not usually cleft so deeply as indicated by Garman; teeth numerous, 
close-set in double ranks; eye large, elevated, round or but slightly oval, 4.0-4.3 
in the head, orbital bones forming a prominent ring; cheek more squarely angulate 
below than other species; opercle wide-angled, slightly eared. 
Seales thickened, cornified, smooth, close-set; crown completely armored; 3-6 
infraorbital scales, variable; cheek scaled in three rows; naked areas sometimes 
along sides of back; vertebral series 13-14; prepectoral scales generally dehiscent, 
and differing also from Valenciennes’ figure in that the naked preventral area 
extends to the base of the pectoral fin; many with more or less complete scalation 
on venter, with the flattened preventral area back of the isthmus bearing a band 
of scales. 
Fins of the flexible, parchment type; origin of the dorsal fin shghtly nearer 
the caudal basis than to occiput; dorsal and anal rather small, both 13-14; caudal 
rather long, especially in the young, 28-30; pectoral 15-16, long, narrow, reaching 
considerably beyond half way to the origin of the anal fin. 
The young begin to be identifiable at 40 mm., lighter, more slender, less 
elevated. 
This species and O. owenii share between them the property of having the 
anterior half more developed, the caudal half weak; differing in the longer, more 
rounded snout, less elevation, smaller eye, rounded chin and convex ventral con- 
tours, feeble armament, of owenit. 
Colors uniform dark brown on dorsal and caudal parts, a faint lateral stripe, 
greenish-yellow below, brightest on cheek, opercle, and shoulder; fins uniformly 
light-rayed with darkened membrane between rays. 
Valenciennes’ record from Lake Titicaca is doubtful. 
Known to inhabitants as /sp7, or Hispe. 
