212 MEMOIRS OF THE CARNEGIE MUSEUM 



Thrychomyderus Cuvier and Valenciennes, Hist. Nat. Poiss., XVIII, 1846, 485 



(misquoted). 

 Thrichomyderus Girard, U. S. Nav. Astron. Exped., II, 1855, 242 (misquoted). 

 Pygidmm Meyen, Reise in Peru, I, 1835, 475 ifuscum). 



Type, Pygidium fuscuni Meyen. 



Origin of the dorsal over or in front of the origin of the short anal; gill-mem- 

 branes free from the isthmus; mouth terminal; ventrals present; two maxillary 

 barbels; nasal barbels; opercle and preopercle with osseous prickles. 



Key to the Guiana Species of Pygidium. 



a. Origin of dorsal in front of the vertical from the origin of the anal; maxillary barbel reaching tip of 



opercle; snout about 2.5 in the head; nasal barbel reaching not quite to the tip of the maxillary 



barbel. 



b. Head 6 in the length; the first pectoral ray with its filament equals the length of the head; sides 



and back with numerous spots, each larger than the eye, in about five series between the 



dorsal and anal guianense. 



bb. Head 5 in the length; first pectoral ray with its filament equals the length of the head without 



the opercle; uniform yellowish brown above, lighter below; top of head marbled . . . conradi. 



aa. Origin of anal under origin of dorsal, head 6 in the length; maxillary barbel reaching tip of pectoral, 



outer pectoral ray with its filaments equals the head in length; upper parts obscurely 



spotted gracilior. 



82. Pygidium guianense Eigenmann. 



Pygidium guianense Eigenmann, Ann. Carnegie Mus., VI, 1909, 11 (Aruataima, 



on the Potaro); Repts. Princeton Univ. Exp. Patagonia, III, 1910, 400. 



This species is known from the type, taken in the cataracts of the Potaro River, 

 above the Kaieteur. 



Type, 77 mm. Aruataima Falls, Upper Potaro. (Carnegie Museum Catalog 

 of Fishes No. 1003.) 



Head 6; depth equals head in length; D. 9; A. 7; eye 4 in snout, 9.5 in head. 



Head nearly as broad as long; maxillary barbel reaching to tip of opercle; 

 teeth in bands of about four irregular series; origin of anal under middle of dorsal; 

 dorsal fulcra extending forward to near the dorsal; caudal rounded; first pectoral 

 ray prolonged in a filament nearly as long as the rest of the ray; round dark spots 

 everywhere, except on belly and lower surface of head ; caudal dusky, the margin 

 light. 



83. Pygidium conradi sp. no v. 



Pygidium guianense Eigenmann, Ann. Carnegie Mus., VI, 1909, 11, part (Ama- 

 tuk and Waratuk), 



