ON THE ICHTHYOLOGY OF LAKE TITICACA. 



181 



4. Orestias frontosus, Cope, sp. uov. 



Fin radii D. 14-15 ; A. 15. Scales of lateral line (commencing above preoper- 

 culum), thirty-six. Dorsal region little arched, frontal region protuberant and 

 convex in both longitudinal and transverse section, the profile then descending 

 steeply to the upper lip. Mouth nearly vertical, eye four times in length of head 

 of specimens eight inches long. The depth of the head at the posterior border of 

 the orbits is exactly equal to the length, and its length is contained in the total 

 (without caudal fin), four times in one, and three and three-quarter times in 

 another specimen. The preorbital bone is higher than long, and the inferior 

 border of the preoperctilum is two-thirds the length of the posterior. Large, 

 thickened, and smooth scales cover the anterior part of the body, and the oper- 

 culum, preoperculum, and suborbital bones, and advance on the front to between 

 the orbits. The depth of the body enters the length three and one-third times. 



Tail even or slightly convex, 



M. 

 Total length . . . , 0.190 



Length to basis of anal fin 



" of head . 



" to orbit . 

 Interorbital width (axial) 



.103 

 .038 

 .010 

 .016 



This Orestias is generally black, the belly having a pale yellowish color. 



Its affinities are to the O. ortonii, but the difi"erence in the form of the head is 

 very striking. Dr. Giinther describes the head of the O. owenii as deeper than 

 long, and the posterior border of the preoperculum as equal to the lower, charac- 

 ters not possessed by the O. frontosus. 



Two specimens were obtained by Prof. Orton, who states that they are called 

 by the inhabitants "Caracha," while the O. hairdii and 0. pentlandii are known as 

 " Boga," and adds that all are excellent table fishes. 



