Family III. Silurid^e. 21 



midway between base of caudal and base of next to last dorsal ray; 

 caudal fin forked, its lower lobe broad and round, its upper pointed; 

 fontanelle reaching middle of orbit ; dorsal fin slightly higher than long, 

 its base if in head; dorsal spine weak, flexible, its length 1^ in base 

 of fin; pectoral fin small, its spine strong, with small teeth on its 

 outer margin, the largest being near its tip, the inner margin ser- 

 rate, except the portion nearest tip opposite the large teeth on 

 outer margin; pectoral spine 2§ in head; length of adipose fin 2% in 

 body; ventrals inserted opposite last dorsal ray. 



Color uniform dull brownish, slightly lighter on the lower half of 

 the body; a narrow black lateral band; dorsal fin with a light cross- 

 band occupying the second fourth of the fin from base; no dark dots. 



This species reaches a length of about 18 inches. It is very 

 abundant in the streams of Mexico south of Vera Cruz. 



17. Rhamdia laticauda (Heckel). 



Pimelodus laticaudus Heckel, in Kner, Sitz. Wien, Ac, xxvi, 

 420, 1857; Mexico: Gunther, Cat., v, 127, 1864. 



Rhamdia laticauda Jordan & Evermann., Bull. 47, U. S. Nat. 

 Mus., 1896, 152. 



Head \]A,\ D. I, 6; A. 13. Body elongate; head covered with soft 

 skin above; occipital process short; lower jaw the shorter; the eyes 

 situated somewhat before the middle of the head, their diameter § 

 width of interorbital ; pectoral spine only half as long as rays; base 

 of adipose 3K m body; caudal peduncle nearly as deep as body; 

 caudal fin subtruncate. (Kner.) 



We know this species only from the above account. 



18. Rhamdia brachyptera (Cope). 



Pimelodus brachypterus Cope, Trans. Amer. Phil. Soc, 1866, 404; 

 Orizaba, Mexico. 



Rhamdia brachyptera Jordan & Evermann, Bull. 47, U. S. Nat. 

 Mus., 1896, 151. 



Mountain streams of the south central portion of Vera Cruz. 

 (Motzorongo.) 



Head 4|; depth 5; D. 1, 7; A. 10. Body rather elongate, robust 

 anteriorly, compressed posteriorly; back slightly elevated; head 

 elongate, rather narrow, flattened with rather steep sides; snout 

 little broader than long, its length 2% in head; eye small, high up on 

 head, directed outward and upward; diameter of eye 5%" in head; 

 width of mouth 2 l A > ; teeth small, sharp, conic; interorbital 2^; 

 maxillary barbel short, its tip reaching base of ventral; outer mental 

 barbel extending to the tip of the humeral process ; fontanelle extend- 



