68 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY II. 



n. Dorsal fiu beginning entirely behind ventrals : 

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

 small, inferior; anal basis short .. (Su bgenus ?) Codoma, 14. 

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

 head more or less pointed ; anal basis somewhat elongate, 



NOTOTROPIS, 15. 

 nn. Dorsal fin beginning above some part of ventrals ; aspect of 



Nototropis Cliola, 1G. 



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

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

 i?sox-like ; scales not 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), 



Ptychochilus, 17. 



tclc. Lips thin; lateral line incomplete or wanting Pkotoporus, 18. 



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

 finbeginningslightly anterior to ventrals; teeth one-rowed ; 



lateral line comi^lete 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 ventrals ; 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 not 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 (^Gila) or 

 eastern species of slender form and small size ( Clinostomus\ 

 or western species of large size, intermediate in form and 

 with the exposed surfaces of the scales broad (Tigoma), 



Gila, 2^. 

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



Siboma, 23. 

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



to. Dorsal over ventrals: body rather stout Myloleucus, 24. 



ivw. 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 fin entirely behind ventrals ; lateral line decurved, 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 Lavinia, 26. 



* To this genus I refer at present Tigoma pulehra, T. nigrescens, and T. gibhosa 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. 



