186 



ON THE ICHTHYOLOGY OF LAKE TITICACA. 



more elongated body and shorter fin bases. The head, according to Giinther, is 

 one-third the length in that fish, and the. radii are A. 14-16 ; D. 18-19. It is 

 dedicated to Professor Spencer F. Baird, the assistant secretary of the Smithsonian 

 Institution, the alma muter of many naturalists of the present and coming gene- 

 rations. 



3. Oeestias oktonii, Cope, sp. nov. 



Radii of the fins, P. 18; D. 16; A. 16. Dorsal outline gently arched to 



interorbital region, muzzle horizontal, narrowed, the mouth directed vertically 



upwards. Length of head one-fourth the total, minus the caudal fin, the greatest 



depth entering the same three and one-third times. Eye four and a half times in 



the length of the head, and twice in the interorbital width. Lower limb of preo- 



percle three-fourths as long as the posterior. Scales of lateral line, beginning 



above anterior part of operculum, thirty-two. On the anterior part of the body 



they are thickened and enlarged, there being but eight rows from the base of 



superior ray of pectoral fin to the median nuchal row. They extend forwards to 



between the eyes, and cover the entire operculum, preoperculum, and suborbital 



bones. All are entirely smooth. The dorsal fin is further from the caudal than 



the length of its base. Preorbital bone deeper than long. 



M. 

 Total length 162 



.133 



Length to basis caudal fin 



" to basis anal fin 



" to operculum . 



" to preoperculum 



to orbit . 



Depth of head at orbit 



.082 

 .033 

 .022 

 .008 

 .026 



Color silvery, the enlarged scales of the anterior part of the body green; head 

 above black, sides yellow. 



This species appears to be most nearly allied to the Orestias owenii, Cuv. Val., 

 in the proportions of the head to the body, but the head is of a different form. 

 Giinther states that the head of O. owenii is "nearly three-fourths as long as high;" 

 in O. ortonii it is two- thirds. as high as long. The caudal peduncle is longer in 

 O. ortonii, and the fin-rays of O. owenii are stated to be D. 14-5 ; A. 13-6. In 

 O.jussicei the body is shorter by one length of the head, and the radii are D. 14 ; 

 A. 15. 



This species is dedicated to Professor James Orton, of Vassar College, the 

 indefatigable explorer of the Peruvian Andes. 



