286 



U. S. P. R. R EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



extremity does not reach the insertion of the ventrals in the female, whilst in the male they 

 extend beyond. 



D 1, 9 ; A 1, 9 ; C 8, 1, 8, 8, 1, 7 ; V 1, 9 ; P 15. 



The scales are quite diversified, being of different sizes, according to the regions of the body. 

 They are very small on the dorsal region between the occiput and the dorsal fin, increasing 

 somewhat in size between the dorsal and the caudal, and becoming almost uniform along the 

 peduncle of the tail. They are largest along the flanks, whilst they are again reduced in size 

 on the belly from the throat to the anal fin. In shape they are sub-elliptical, anteriorly 

 truncated, or undulated, longer than deep, exhibiting radiating furrows, not only upon the 

 posterior section, but likewise laterally. The lateral line is very conspicuous, slightly deflexed 

 along the flanks, where it is equidistant between the dorsal and abdominal outlines, to the 

 very base of the caudal fin. 



The color is uniformly greyish brown above and yellowish beneath. The fins assuming the 

 tints of the region of the body to which they belong. 



List of specimens. 



2. GILA ELEGANS, B. & G. 



SPEC. CHAR. Body very slender ; tail very much attenuated. Head constituting the fifth of the total length. Eye small, 

 sub-elliptical ; its diameter entering seven times in the length. Posterior extremity of maxillar bone extending to a vertical 

 line drawn in advance of the orbit. Anterior margin of dorsal fin nearer the extremity of the snout than the base of the caudal. 

 Base of anal fin entering about nine times in the total length. Origin of ventrals much nearer the extremity of the snout than 

 the base of the caudal. Reddish brown above ; metallic yellow beneath. 



STN. Gila elegants, B. & G. in Proc. Acad. Nat. Sc. Philad. VI, 1853, 369 ; and, in Sitgr. Rep. Zuni and Color. Rivers, 

 1853, 150, pi. ii. GRD. in Proc. Acad. Nat. Sc. Philad. VIII, 1856, 205. 



The most striking peculiarity of this species consists in its elongated and slender body, and 

 especially its slender tail, terminated by a rather well developed and deeply furcated caudal fin. 

 Indeed, all the fins are proportionally well developed. The greatest depth in advance of the 

 dorsal enters seven times in the total length. The greatest thickness being about the half of the 

 depth. 



The head is very much depressed, flattened upon the snout, forming the fifth of the total 

 length. The eyes are sub- elliptical, their diameter entering seven times in the length of the 

 side of the head, and twice between the tip of the snout and the anterior rim of the orbit. 

 They are more apparent upon a view of the head from beneath than from above. The nostrils 

 are situated entirely upon the upper surface of the snout, further apart from the extremity of 

 the latter than the eye. The mouth is inferior ; the upper jaw overlapping the lower. The 

 posterior extremity of the maxillar bone extending to a vertical line drawn in advance of the 

 orbit. The isthmus is very small. 



The rays in all the fins have the same general structure as in the preceding species ; the 

 dorsal and anal are provided anteriorly with three rudimentary rays instead of one, and the pos 

 terior margins of either of these fins is much lower than the anterior margin as compared to the 



