FIfeHES—CYPRINIDAE— GILA ROBUSTA. 
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four others; the latter was erected into a distinct genus under the name of Orthodon ; and, 
what is still more curious, Orthodon belongs to the tribe of Chrondostomi, hence its affinities 
with Gila are most remote. 
The three species of Gila described hereon are admirably figured in Captain Sitgreaves’ 
“ Eeportofan Expedition down the Zuni and Colorado Eivers, 1853.” The other species known up 
to the present time, two in number, are figured in the “ Eeport on the United States and 
Mexican Boundary Survey, vol. II.” 
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 side 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 than 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. 
Syn.— Gila robusta, B. & G. in Proc. Acad. Nat. Sc. Philad. YI, 1853, 368 ; and, in Sitgr. Rep. Zuni and Color. Riv. 1853, 
148 ; Fishes, pi. I. —Grd. in Proc. 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 occiout 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 hone does not reach a vertical line drawn in advance of the pupiL 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 he 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 ib 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 
