Art. VII. — Note on the Ichthyology of Lake Titicaca. 



By E. D. Cope. 



The waters of the elevated plateaus of the Andes have been found to be the 

 habitat of several peculiar genera of fishes, mostly belonging to the SiluridcE and 

 the Cyprinodontidce. Of the latter family two genera are now known, Protistius^^ 

 Cope, with one species from the Peruvian Andes, and Orestias (Cuvier and Valen- 

 ciennes), of which six species have been described from the Lake Titicaca in the 

 Bolivian plateau. Prof James Orton, in his recent exploration of that region, 

 procured specimens of four species of this genus from the Lake. On examination 

 of these I find, unexpectedly to myself, that three of the species are new to science, 

 and accordingly append descriptions of them. They are all in fine condition, and 

 apparently adult. 



1. Orkstias pentlandii, Cuv. Val., Vol. XVIII, p. 221. 



2. Orestias bairdii, Cope, sp. nov. 



Established on a specimen eight and three-quarter inches long. Eadii P. 17; 

 D. 12- A. 16. Scales of the lateral line, counting from the line of the preoper- 

 culum, fifty. Scales larger above the operculum and rugose in that region, else- 

 where smooth. Operculum about half covered with rugose scales; the lower limb 

 of the preoperculum half as long again as the posterior, the scales small, rugose, 

 and extending its entire length, leaving a naked band below the orbit. A few 

 small, rough scales on the preorbital bone. Preorbital bone subquadrate, as long 

 as high. Mouth directed vertically upwards. Top of the head entirely naked. 

 A band of large rugose scales on the nape, with a naked space on each side of it. 



The diameter of the eye is equal to the length of the muzzle, and enters the 

 side of the head five times. The outline^ of the back and head is continuous and 

 horizontal, the front flat, and over twice the long diameter of the eye. The head 

 enters the length, minus the caudal fin, four and a quarter times, and the depth 

 enters the same four and a half times. The depth of the head enters its length 

 14 times. The dorsal fin is further from the anal than the length of its base, and 

 the margin of the caudal fin is openly concave. 



This species is evidently nearest to the 0. cuvieri of Valenciennes ; it has a 



* Proceedings Academy Philada. 1814, p. 66. 

 41 (185) 



