FIbHES CYPRIKIDAE GIL A KOBUSTA. 285 



four others ; the latter was erected into a distinct genus under the name of Ortlwdon ; and, 

 what is still more curious, Ortlwdon belongs to the tribe of Cltrondostomi, hence its affinities 

 with Gila are most remote. 



The three species of Gila described hereon are admirably figured in Captain Sitgreaves 

 1 Eeport of an Expedition down the Zuni and Colorado Eivers, 1853. The other species known up 

 to the present time, two in number, are figured in the &quot;Eeport on the United States and 

 Mexican Boundary Survey, vol. II.&quot; 



1. GILA EOBUSTA, B. & G. 



SPEC. CHAR. Body sub-fusiform, anteriorly stout, posteriorly tapering. Head constituting the fourth of the total length. 

 Eye small, sub-elliptical ; its diameter entering about eight times in the length of the siiie of the head. Posterior extremity of 

 maxillar bone extending to a vertical line drawn somewhat within the anterior rim of the orbit. Anterior margin of dorsal fin 

 nearer the insertion of the caudal lhan the extremity of the snout. Base of anal fin entering nine times and a half in the 

 total length. Origin of ventrals nearly equidistant between the extremity of the snout and the insertion of the caudal. 

 Greyish brown above ; yellowish beneath. 



STN. Gila robusta, B. & G. in Proc. Acad. Nat. Sc. Philad. VI, 1853, 368 ; and, in Sitgr. Rep. Zuili and Color. Riv. 1853, 

 148 ; Fishes, pi. I. GRD. in Prec. Acad. Nat. Sc. Philad. VIII, 1856, 205. 



The general shape of the body is sub- fusiform, very much swollen anteriorly, and tapering 

 very suddenly from the dorsal fin towards the base of the caudal. The body itself is com 

 pressed*; its greatest depth is midway between the occiput and the anterior margin of the dorsal. 



The head is very much depressed above, rapidly sloping from the nape to the snout. The 

 side of the head enters four times in the total length, whilst its crenial region enters in it six 

 times. The eyes are rather small, longitudinally elliptical ; their diameter entering about eight 

 times in the length of the side of the head, and thrice from the tip of the snout to the pupil. 

 The nostrils are large, situated towards the upper aspect of the head, and placed nearer the 

 orbit than the extremity of the snout. The mouth is rather large ; the upper jaw overlapping 

 the lower ; both being surrounded with quite conspicuous lips. The posterior extremity of the 

 maxillar bone does not reach a vertical line drawn in advance of the pupil 3 although it extends 

 beyond the anterior rim of the orbit. There are three branchiostegal rays on either side, broad, 

 flattened, closely approximated. The gill openings are quite large, being separated beneath by 

 a very narrow isthmus. The mucous pores on the head are not conspicuous ; a series, however, 

 more apparent than the rest, may be traced from occiput to snout, in passing under the orbit. 



The dorsal fin, which is inserted exactly upon the middle of the total length, is somewhat 

 higher than long and slightly concave upon its upper margin ; its posterior margin is half 

 the height of the anterior margin. All but the anterior ray dichotomize thrice, although the 

 branches of the third bifurcation remain in close contiguity. The posterior margin of the 

 caudal is crescent-shaped, the upper and lower lobe being symmetrical ; the sixteen median 

 rays are dichotomized in the same manner as those of the dorsal fin. The insertion of the anal 

 takes place immediately behind the base of the dorsal, and of which it has the same general 

 shape, being deeper than long and slightly concave exteriorly ; its posterior margin, however, 

 has but one-third of the depth of the anterior margin. The rays are bifurcated like those of 

 the dorsal. The ventrals are exteriorly rounded, nearly equidistant between the extremity of 

 the snout and the insertion of the caudal fin, and when bent backwards they scarcely reach the 

 vent. Their rays affect the same structure as in the other fins. The pectorals are very broad 

 when expanded, and their rays thrice dichotomized. When bent backwards their posterior 



