296 MEMOIRS OF THE CARNEGIE MUSEUM. 



Known from the type, a specimen 85 mm. long, in the National Museum at 

 Buenos Aires. 



Head 8.5 in the length with the caudal; D. 9 (2 + 7); A. 7 (1 + 6); eye 1.5 in 

 the snout, 1.5 in interorbital, 2.5 in posterior part of the head; nasal barbel scarcely 

 extending beyond the eye; maxillary barbel scarcely to end of opercle; gill-membrane 

 with scarcely a free margin ; intero]Dercular spines in two or three series, medium in 

 size; teeth small, in irregular series, anterior ones larger, their tips broader; fins 

 small; first pectoral ray prolonged; anal under last third of dorsal; caudal truncate. 



10. Pygidium heterodontum Eigenmann. (Plate XLIV, fig. 4.) 

 Pygidium heterodontum Eigenmann, Proc. Am. Philos. Soc, LVI, Jan., 1918, p. 



692. 

 13832, 1. U. M., 83 mm., 9, Rio Mcndoza, Palmira, Argentina, 900 m. Purchased 



from Rosenberg. 



Palmira is probably the southernmost locality on the eastern slope of the 

 Andes from which species of this genus have been taken. 



Head six times in length, as long as broad; D. 10.5 (4 + 6.5); A. 7.5 (2 + 5.5); 

 P. 9; eye in middle of the head, intcrocular 3.5 in the head; teeth in three series in 

 each jaw, those of the outer row narrow incisors, of the second row much smaller 

 incisors and of the third row conic. Head much depressed, interopercular spines 

 numerous, thirteen in the last row. 



Nasal barbel extending to the posterior margin of the eye, maxillary barbel to 

 the base of the ojiercular spines; first pectoral ray scarcely produced, equal to the 

 portion of the head behind the posterior nares; origin of ventrals midway between 

 opercle and caudal, reaching to the vent; origin of anal under posterior part of the 

 dorsal, the distance between its last ray and the base of the middle caudal ray 4.4 

 in the length; depth of the caudal ])eduncle 2.5 in its length; caudal narrow, emargi- 

 nate, a httle more than five in the length; origin of dorsal midway between the tip 

 of the caudal and the occiput, over the tip of the ventrals, its distance from the 

 caudal 1.75 in its distance from the snout. 



A faint lateral band and obscure spots or marblings. 



The members of the genus Pygidium reach their largest size and greatest 

 economic importance in Peru. The C'arnegie Museum has no specimens from this 

 region, except P. oroyce Eigenmann & Eigenmann. To the key below should be 

 added P. fuscum Meyen, the type of the genus. 



Key to the Species of Pygidium from Peru and Western Bolivia. 

 a. Pfictoral ray prolonged. 



h. Dorsal entirely in front fif tlic ;inal. 

 c. Caudal truncate or ronniloil. 



