EXPLORATIONS IN COLORADO AND UTAH. 
27 
Head, 4; depth, ; D. 12 ; A. 7. Scales 10-80 to 83-13. 
Bod}^ more elongate than in X. cypho of the same size, the form resembling that 
of a Gila ; head flattish above, narrower and less depressed than in X cypho, the 
snout sharper than in X. cypho, projecting considerably beyond the small month ; 
lips rather small, but rather larger and more coarsely tuberculate than in X. cypho, 
the upper with three rows of papillae, the lower deeply incised. 
Nuchal hump, formed by the expanded iuterueurals, much lower than in X. 
cypho, but forming a sharj) keel. This does not extend forward to the nape, there 
being about thirteen scales before it. Surface of nuchal keel scaly. 
Eye, in head ; snout, 2^ ; interorbital space, 2^. Scales smaller than in X. 
cypho, small anteriorly, growing larger backward ; breast naked ; caudal peduncle 
slender, much slenderer than in X. cypho, its least dei)th in its length and 3f in 
head. Caudal fin large, deeply forked, a little longer than head. Dorsal lower than 
in X. cxjpho ; the longest ray, li in head ; base of fin, 1:|. Pectoral, in head, not 
reaching ventrals ; the latter to vent. 
Color bluish above, pale below. Peritoneum black. 
Type in the IJ. S. National Museum. 
4. Pantosteus delphinus (Cope). Blue-head Sucker. 
Common, especially near the mountains. Specimens taken in Eagle Eiver, Gun- 
nison River at Delta, Uncompahgre Eiver, Eio de las Animas Perdidas, and Rio 
Florida. This species reaches a lengtli of about a foot and is well characterized by 
its small scales and its large lips. Mau^^ die in the rivers after spawning. 
In life, bluish, olive, or gray; lower fins dull orange; several round dashes of 
red along the lateral line, forming an interrupted red band. Scales OG to 105. 
5. Gila robusta (Baird & Girard.) Bound-tail. 
Generally common at the foot of the mountains; replaced by Gila elegans h\ the 
river channels. Found in the Uncompahgre, and in the Gunnison at Delta. 
The species of Gila are very similar to each other and are probably reducible to 
three, G. elegans, G. robusta, and G. seminuda. The last-mentioned I have not seen. 
Our specimens from the Gunnison evidently correspond to Gila robusta. Gilagra- 
hanii B. &, G. seems to be the same. I can not distinguish Gila affinis Abbott from 
Gila robusta. This species has been reported from the Kansas and the Platte, but the 
types doubtless came from Green River, as no recent collectors have found any species 
of this type anywhere except in the basin of the Colorado and Gila Rivers. Gila 
gracilis B. & G. is not evidently different from G. robusta. Gila nacrea Cope, from 
Green River, Wyoming, is evidently the young of Gila robusta. Dr. Gilbert has 
reached independently similar conclusions as to the synonymy of these species. 
Gila robusta reaches a length of more than a foot. It is full of small bones and 
is regarded as worthless for food. The males in life have the lower fins and lower 
side of the head red, and there is a vertical dasli of red on the cheeks. Scales 79 to 
82 in the lateral line, those above and below smaller. 
6. Gila elegans Baird & Girard. Bony- tail. 
One specimen taken in the Gunnison at Delta; five in the Green Eiver. Appar- 
ently not ascending the streams so far as the preceding. 
Comparing specimens of similar size, Gila elegans has a higher nape and back, 
more depressed head, slenderer caudal peduncle, larger fins, and smaller scales on 
