366 FISHES OF WESTERN SOUTH AMERICA 
since the difference might be accounted for by age; the mouth is similar, a rather 
unique character, the light-centered scales of the shoulder, size of eye, paucity of 
teeth. 
Eye small, 5.5 in the head, rounded, equal to luteus in its distance from the 
end of the snout; eye without the protuberant supraorbital; width of head sur- 
passing its depth; head 2.7 in body length; interorbital 2.7 times the eye; crown 
considerably elevated and convex in both dimensions, with a short, flatter area at 
the occipital; snout sometimes expanded to give the effect of a proboscis. 
Scales similar to luteus in the extent and form of the granulations; resembling 
it also in the naked infraorbital, outlined by a row of pores, and snout naked; sur- 
passing it in the investiture of the prepectoral, represented by Valenciennes with 
pectoral fin surrounded by a scaleless area, which Starks makes a diagnostic char- 
acter; cheek scales barely reaching, not passing, the anterior level of the orbit. 
Vertebral series three, regular, as described by Garman, without lateral desqua- 
mated areas. 
D. 14; A. 18-14; P. 19; C. 28. 
While O. luteus belongs to the parchment-finned group of species, those of 
albus are smaller, fleshier, more rigid in alcohol, thick-skinned, and heavily coated 
in mucus. Garman says they are medium, I should say small, with the dorsal 
basis less than its distance from the first caudal finray; pectoral broad; caudal 
deeper than long, its depth half that of trunk, while /uteus exceeds half, and is con- 
spicuously larger; I am unable to find 35 rays as did Valenciennes. 
Sharing with O. luteus the extensible, muscular, unscaled vent region, as 
though used for oviposition. 
Colors in aleohol varying from red-brown to gray-green and nearly black; fins 
colorless or nearly uniformly brown. 
Garman was in error as to Lake Umayo, type locality, being without outlet. 
It drains by a small stream, the Rio Ilpa, to the bay of Puno. 
481. ORESTIAS SILUSTANI Allen, sp. nov. 
Plate XIX, fig. 1 
16097, 5, 55-86 mm., Lago Umayo, Allen, January, 1919. 
Catalogued as O. olivaceus. Comparison with the cotype of the latter brings 
out numerous differences. They resemble one another in the extremely superior 
mouth and convexity of the ventral surface of the head. My type has an even 
straighter dorsal profile with less indication of a predorsal hump; like olivaceus 
the mouth and cheeks widely and roundly expanded, without the angularity of 
luteus, but the width of the head not equal to that of olivaceus; differing from it in 
the smooth, moderately thickened scales of opercle, without the granulations. 
Differing in the lack of the almost uniform green color of olivaceus. The type is 
of the same size as the olivaceus cotype, is more compressed, more tapering, with 
a slenderish caudal peduncle, body form much less expanded and robust. 
My paratypes are sufficiently unlike the type to be mistaken easily for luteus 
