1856.] 207 



Collected by Lt. E. G. Beckwlth, U. S. A. 



B. Teeth provided with a grinding surface more or less conspicuous. 



10. TiGOMA GiBBOSA. OUa gibbosa, B. & G. Proc. Acad. Nat. Sc. Philad. vii, 

 1854, 28. Resembles T. -purpuren^ but its scales are a good deal smaller. 



Specimens were collected near Santa Cruz, by John H. Clark, under Col. J. 

 D. Graham, U. S. A. and at Tuczon, Sonora, by Dr. A. L. Heermann, under 

 Lt. J. G. Parke, U. S. A. 



11. TiGOMA NiGRESCENS This is quite an elegant species, being elongated 

 and slender like T. pulchella and T, gracilis. It differs from T. gibbosa by a more 

 conical head and snout. The ground color is yellftwish, the body of the scales 

 being covered with crowded black dots, the back and sides appear almost black, 

 The belly is unicolor. In the young, the upper regions are lighter than in the 

 adult. 



Specimens were collected in the Boca grande and Janos river, by Dr. C. B. 

 Kennerly under Major W. H. Emory, U. S. A. 



12. TiGOMA PULCHRA. The body is gracefully elongated, in which respect it 

 resembles T. nigrescens, from which it may be distinguished by its smaller head 

 and larger scales. The color, moreover, is of a far more brilliant tj'pe : the 

 dorsal region is reddish or blackish brown, the sides and belly of a uniform 

 golden yellow ; a diffused black streak may occasionally be seen along the 

 upper portion of the flanks, very likely more predominent in the male than in 

 the female. 



Collected in Chihuahua River and tributaries, by John Potts, Esq., of Chihua- 

 hua, Mex. 



13. TiGOMA CRASSA This species has a short and deep body ; the greatest 

 depth being more than the fourth of the entire length. The head is small and 

 conical, constituting nearly the fifth of the entire length of the fish. The scales 

 are very large, higher than long and the lateral line deflexed upon the abdo- 

 men as usually the case in this genus. The color of the back is bluish or 

 purplish black, greyish black on the sides where the yellowish ground color 

 appears ; beneath unicolor. 



Caught in the Sacramento River near Fort Reading, Cal., by Dr. John S. New- 

 berry, under Lt. R. S. Williamson, U. S. A. 



Next to these numerous species in which the system of dentition seems to be 

 in a unstable condition, we place the new genus 



CHEONDA, 



which has the general aspect of both Gila and Tigoma, by the position of the 

 ventrals in advance of the anterior margin of the dorsal, by the absence of barbels 

 at the angle of the mouth, which is of moderate size. 



The body is elongated, fusiform in profile, and very much compressed. The 

 caudal fin is bifurcated. The head is rather small and subconical, and the 

 snout, though rounded, is yet elongated. The eye is large and the isthmus 

 small or narrow. The scales being of medium size and the lateral line greatly 

 deflexed upon the abdomen. The teeth are of the prehensile kind, of the 

 hooked type, with a grinding surface ; they are compressed and disposed upon 

 a double row of two and four and five, thus : 2 | 4 5 | 2. 



1. Cheonda cooperi. The fins are well developed and the anal is larger 

 than the dorsal. Their formula is as follows : 



D 10-hl2 ; A 11 + 2 ; C 7, 1, 9, 8, 1, 6 ; V O-j-l ; P 16, 



The dorsal region is reddish grey ; the sides and belly silvery white, with a 

 golden reflect. 



Collected at Fort Vancouver, Columbia River, by Dr. John G. Cooper. 



2. Cheonda ccerulea. May readily be distinguished from its congener by 



