58 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY—II. 
n. Dorsal fin beginning entirely behind ventrals: 
o. Body short and thick; the head almost globular; the mouth 
small, inferior; anal basis short..(Subgenus?) Copoma, 14. 
oo. Body elonyate, with the month oblique, terminal, and the 
head more or less pointed; anal basis somewhat elongate, 
Nororroris, 15. 
nn. Dorsal fin beginning above some part of ventrals; aspect of 
Nototroprs: |... Joe arent neelaiee x= areas CuioLa, 16. 
ll. Species of large size, wiih the body much elongated, sub- 
cylindrical; the head elongated, and the mouth deeply cleft, 
Esox-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. 
kk. Lips thin; lateral line incomplete or wanting.-.. PROTOPORUS, 18. 
kkk. Lips thick, fleshy, enlarged behind ; mouth small, inferior ; dorsal 
fin beginning slightly anterior to ventrals ; teeth one-rowed ; 
lateral line completé:==-2- .22. 2222522242 PHENACOBIUS, 19. 
jf. 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 
SHOLG seals etter So see ee ec is sores e PHOXINUS, 21. 
pp. Lateral line complete: 
s. Lips normal, without cartilaginous or bony sheath: 
t. Anal basis not elongate—of 10 or fewer rays: 
wu. 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 (Clinostomuay 
or western species of large size, intermediate i form and 
with the exposed surfaces of the scales broad (Tigoma), 
GILA, 22. 
vv. Dorsal over ventrals ; mouth smaller ; body stout and heavy, 
SIBOMA, 23. 
wu. Teeth not crenate, raptatorial, with grinding surface : 
w. Dorsal over ventrals; body rather stout. .... MYLOLEUCUS, 24. 
ww. Dorsal entirely behind ventrals; body more elongate, com- - 
pressed j,.sucectk ater sess 25 elosee eo aes 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 elonvate; large: --o-.~------ == ee LAVINIA, 26. 
*To this genus I refer at present Tigoma pulchra, T. nigrescens, and T. gibbosa 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. 
