FAMILY IV. CATOSTOMID.E. 35 



Head 4f; depth 4; D. n; A. 7; scales 7-45-5. Body elongate, 

 terete; head large; interorbital area flat, its width 2 in the length of 

 the head; eye 4^; snout 2>; origin of dorsal fin midway between tip 

 of snout and tip of last anal ray; about 16 scales in a series before 

 dorsal fin; margin of dorsal- fin slightly concave, the length of its first 

 rays i % in head , its base i % ', shortest dorsal ray 2 X ! caudal fin forked , 

 its lower lobe slightly the larger; longest caudal ray 1% in head; 

 length of pectorals equals the length of the head ; distance from tip of 

 pectorals to base of ventrals 5^ in length of pectoral; ventrals if 

 in head, their tips reaching ^ distance to anal fin; least depth of 

 caudal peduncle 2^ m head. 



Color light olivaceous above, lighter below; middle of each scale 

 silvery, forming faint longitudinal stripes along rows of scales; dorsal 

 membranes blackish; other fins plain. Length 12 to 14 inches. 



This species has not been taken in the Rio Nazas or in other iso- 

 lated bodies of water in northern Mexico. 



31. riyzostoma austrinum Bean. 



Myxostoma austrina Bean, Proc. U.S. Nat. Mus., 1879, 302; La 



Piedad in Morelia, Michoacan. 



Moxostoma austrinum Woolman, Bull. U. S. Fish Comm., 1894, 

 61; Rio Lerma, Salamanca, Guanajuato: Jordan & Evermann, 

 Bull. 47, U. S. Nat. Mus., 1876, 192: Jordan & Snyder, Bull. 

 U. S. Fish. Comm., 1900, 120; Rio Verde, Aguas Calientes; 

 Rio Santiago, Ataquiza, Jalisco: Meek, Field Col. Mus. Pub. 65, 

 1902, 76; Ocotlan; La Palma. 



Basin of the Rio Lerma and headwaters of the Rio Mezquital. 

 (Durango.) 



Head 4^ to 4$; depth 4; D. n ; A. 6; scales 7-44 to 48-6. Body 

 rather stout; head rather small; interorbital area 2% in head; eye 4^2 

 to 6 ; snout 2 % ', origin of dorsal fin midway between tip of snout and 

 base of last anal ray; 16 scales in series before dorsal fin; margin of 

 dorsal fin slightly concave, its longest ray i in head; base of dorsal 

 1 1 in head; shortest dorsal ray 2> in head; caudal fin forked, lobes 

 about equal ; the length of the pectorals equals the length of the head ; 

 distance from tip of pectoral to base of ventrals 2^ in length of pec- 

 toral; ventrals if in head, their tips reaching % distance to vent; 

 least depth of caudal peduncle 2^\ in head. 



Color light brown above, lower parts yellowish white; dorsal mem- 

 brane blackish, other fins plain.. Length about 15 inches. 



