EIGENMANN: THE FRESHWATER FISHES OF BRITISH GUIANA 



241 



107. Ancistrus lithurgicus sp. nov. 26 (Plate XXV, fig. 3.) 

 Ancistrus lithurgicus Eigenmann, Repts. Princeton Univ. Exp. Patagonia, III, 



1910, 411 (name only). 



Type, 95 mm. Crab Falls. (Carnegie Museum Catalog of Fishes No. 1524.) 



Cotypes, fifteen specimens, 31-88 mm. Crab Falls. (C. M. Cat. No. 1525a-d; 

 I. U. Cat. No. 11950.) 



Head 2.8; much depressed; depth at tip of occipital process 6.8 in the length; 

 width of head an orbital diameter less than its length; interorbital 2.8-3 in the 



Fig. 36. Ancistrus lithurgicus Eigenmann. Type. C. M. Cat. No. 1524. 



head; mandibular ramus 2-2.4 in the interorbital; D. 1,7; A. 1,4; eye 6 in the 

 head in the largest specimen. Ten to twelve spines on the opercle, the longest 1.6 

 in the interorbital. 



Tentacles profuse, the naked area of the snout in the male reaching half-way 

 to the posterior margin of the eye; five or six plates between the dorsals, eleven 

 behind the anal, and twenty-three or twenty-four along the sides. 



Last dorsal ray reaching adipose; base of dorsal about equal to its distance 

 from the tip of the adipose; dorsal spine equal to snout and orbit; lower dorsal 

 ray an orbital diameter less than the head. 



Black; a few minute white dots on back and fins, more numerous on belly, 

 sometimes quite obscure; all fins black, the dorsal and caudal margined with white 

 or yellow. 



Allied to A. hoplogenys, but much more depressed. 



26 Acanthicus, another genus of this subfamily, is represented in the Rio Branco basin of Guiana by 

 Acanthicus hystrix Spix. 



