eigenmann: the FRESHWATER FISHES OF BRITISH GUIANA 281 



This species — if all the above specimens represent one species — differs greatly 

 in different localities. Specimens from the Guiana plateau, for instance, have a 

 dusky blotch above the pectoral, those in the lowlands do not. Some have the 

 dark band extended to the eye, others to the edge of the opercle, and still others 

 to a short distance behind the opercle. The fins also differ very greatly. A final 

 decision cannot be given as to the identity of the specimens on account of the 

 difference in size in examples coming from different places. 



Subfamily Nannostomatin^e. 

 Nannostomus Gunther. 

 Nannostomus Gunther, Proc. Zool. Soc. London, 1872, 146. 



Type, Nannostomus beckfordi Gunther. 



Skull truncate; no occipital process; no fontanel, no lateral line; no adipose 

 fin; jaws equal; teeth broad at top, with several points of equal length. Minute 

 fishes. 



136. Nannostomus beckfordi Gunther. 

 Nannostomus beckfordii Gunther, Proc. Zool. Soc. London, 1872, 146 (Gottver- 



wagting Plantation, a short distance east of Georgetown). — Eigenmann, 



Repts. Princeton Univ. Exp. Patagonia, III, 1910, 427. 



Head 3.6; depth 4.25; D. 8; A. 10; lateral line 22; transverse line 5 between 

 dorsal and ventral. 



Body compressed. Eye one-third of the length of the head, and a little longer 

 than the snout. Origin of the dorsal and ventral fins in the middle of the length 

 (without caudal). A silvery band along the middle of the side, bordered above 

 by a reddish, and below by a blackish band. A black spot on the lower half of the 

 gill-cover. Caudal fin red. 



Total length 30 mm. 



This species is readily distinguished by the dark spot on the lower half of the 

 opercle. 



137. Nannostomus marginatus Eigenmann. (Plate XXXVI, fig. 4.) 

 Nannostomus marginatus Eigenmann, Ann. Carnegie Mus., VI, 1909, 41. 



Type, 26 mm. Maduni Creek. (Carnegie Museum Catalog of Fishes No. 

 1171.) 



Cotypes, ten specimens, 21-25 mm. Maduni Creek. (C. M. Cat. No. 1172a-d; 

 I. U. Cat. No. 11696.) 



Cotypes, five specimens, 19-24 mm. Lama Stop-Off. (C. M. Cat. No. 

 U73a-b; I. U. Cat. No. 11697.) 



