68 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY II. 



n. Dorsal flu beginning entirely beliiud veutrals: 

 0. Body short and thick ; the head almost globular; the mouth 

 small, inferior; anal basis short. .(Subgenus?) Codoma', 14. 

 00. Body elongate, with the mouth oblique, terminal, and tho 

 head more or less pointed ; anal basis somewhat elongate, 



NOTOTROPIS, 15. 

 nn. Dorsal fiu beginning above some part of veutrals ; aspect of 



Nototropis Cliola, 16. 



II. Species of large size, with the body much elongated, sub- 

 cylindrical ; the head elongated, and the mouth deeply cleft, 

 Esox-like ; scales uot large ; pharyngeal bones long and slen- 

 der, the teeth slightly hooked (sometimes 4-5) (voracious 

 species of large size and strong organization, aspect of Gila), 



PXYCIIOCHILUS, 17. 



kk. Lips thin; lateral line incomplete or wanting Protopohus, 18. 



kkk. Lips thick, fleshy, enlarged behind ; mouth small, inferior ; dorsal 

 fiu beginning slightly anterior to ventrals; teeth one-rowed; 



lateral line complete Phenacobius, 19. 



ff. Teeth in the principal row 4-5 or 5-5 (or 4-4 in some species referred to 

 Hemitremia) : 

 p. Lateral line incomplete: 



q. Dorsal over veutrals ; scales large ; teeth with grinding surface ; ali- 

 mentary canal short Hemitremia, 19, 



qq. Dorsal behind ventrals; scales small: 

 r. Teeth with grinding surface, one-rowed ; alimentary canal long, 



Chrosomus, 20. 

 rr. Teeth without grinding surface, two-rowed ; alimentary canal 



short Phoxinus, 21. 



pp. Lateral line complete : 



s. Lips normal, without cartilaginous or bony sheath: 

 t. Anal basis uot elongate — of 10 or fewer rays: 

 u. Teeth raptatorial, entire, without grinding surface: 

 V. Dorsal entirely behind ventrals; mouth large; scales small; 

 body elongate; western species of large size with flattened 

 head, arched back, and slender caudal peduncle (Gj7«) or 

 eastern species of slender form and small size {CUnostoinus\ 

 or western species of large size, intermediate in form and 

 with the exposed surfaces of the scales broad {Tigonia), 



Gila, 22. 

 vv. Dorsal over ventrals ; mouth smaller ; body stout and heavy, 



SiBOMA, 23. 



uu. Teeth not crenate, raptatorial, with grinding surface : 



tv. Dorsal over ventrals; body rather stout Myloleucus, 24. 



WW. Dorsal entirely behind ventrals; body more elongate, com- 

 pressed Cheonda,* 25. 



tt. Anal basis elongate, of 11 to 25 rays; body much compressed; dor- 

 sal flu entirely behind veutrals ; lateral line decurvod, com- 

 plete : 

 X. Teeth one-rowed, not serrate, sharp-pointed, with masticatory 

 surface, little hooked ; base of caudal with many accessory 

 rays ; body elongate, large Lavixia, 26. 



* To this genus I refer at present Tifjoma }yuJclira, T. mgrescens, and T. gihbosa of 

 Girard. Cheonda differs from Myloleucus only in the more backward position of the 

 dorsal and from Gila (Tigoma) in the presence of grinding surfaces on the teeth. 



