184 Bulletin 47, United States National Museum. 



94. XYRAUCHEN, Eigenmann & Kirsch. 

 (RAZOR-BACK SUCKER.) 



Xyrauchen, EIGENMANN & KIRSCJT, Proc. U. S. Nat. Mus., 1888, 556, (cypho). 



Characters of the genus Catostomus in all respects except that behind 

 the occiput is a sharp-edged hump produced by the singularly developed 

 interneural bones. The anterior "portion of the hump is supported by a 

 large interneural formed by a thick central pillar with anterior and pos- 

 terior wings, the former coming to a point on the medial projecting plate 

 of the supraoccipital, forming a large opening beneath it; the latter wing 

 is somewhat smaller and articulates with the second interneural. This 

 interneural is a thin, flat, subrectangular plate ; the next is an irregular, 

 flat plate about % as large as the second, while the next 3 are small, 

 flat plates above and bent forward. Other bones of the anterior part of 

 the skeleton are somewhat modified in form, but the essential character 

 of the genus is in the great development of the bones at the nape, show- 

 ing externally as a sharp-edged hump. Two species known ; large suckers 

 of the Colorado basin, (fypbc, razor* avxqv, nape.) 



o. Scales aboiit 13-73-13 ; dorsal rays 13 or 14. Body deep, the back high, the hump com- 

 mencing at the nape with no scales before it or on its edge. CYPHO, 300. 



aa. Scales 16-81-13 ; dorsal rays 12 ; body more slender, the hump much lower ; scales present 

 before it and on its edge. UNCOMPAHGRE, 301. 



300. XYRAUCHEN CTPHO, (Lockington). 

 (RAZOR-BACK SUCKER ; HUMP-BACKED SUCKER.) 



Head 4 ; depth 4. D. 13 or 14 ; A. 7. Scales 13 to 15-72 to 77-13. Body 

 stout, compressed, the head low, the profile ascending to the prominent 

 hump, which is largest in adult specimens and usually begins at the nape 

 with no scales before it, its anterior edge straight, sharp, and scaleless; 

 mouth wide, inferior ; upper lip with 2 rows of papillae ; lower lip deeply 

 divided, with 8 rows. Dorsal long and low, with concave edge; caudal 

 broad and strong, with numerous rudimentary rays ; pectorals moderate. 

 Scales loosely imbricated. Pharyngeal teeth small, numerous ; peritoneum 

 black. Coloration plain olivaceous. Basin of the Colorado and Gila 

 rivers ; very abundant where the water is not too cold ; reaching a weight 

 of 8 to 10 pounds, (cypho, hunchback.) 



Catostomus cypho, LocKiNGTON fc Proc. Ac. Nat. Sci. Phila., 1880, 237, Colorado River at mouth 



of Gila, Arizona. 



Catostomus cypho, JORDAN & GILBERT, Synopsis, 129, 1883. 

 Xyrauchen cypho, KIRSCH, Proc. U. S. Nat. Mus., 1888, 556; JORDAN, Bull. U. S. Fish Com., 1889, 26. 



301. XYRAUCHEN UNCOMPAHGRE, Jordan & Evermann. 



Head 4; depth 4fc. D. 12; A. 7. Scales 16-81-13. Body more elongate 

 than in X. cypho of the same size, the form resembling that of a Gila; 

 head flatter, narrower, and less depressed than in X. cypho, the small lips 

 rather larger and more coarsely tuberculate. Nuchal hump much lower 

 than in X. cypho, but forming a sharp keel which does not extend for- 

 ward to the nape, there being 13 scales before it, its surface also scaly. 



