330 MEMOIRS OF THE CARNEGIE MUSEUM 



This genus differs from Hemigrammus much as Hemibrycon differs from 

 Astyanax. 



Lateral line incomplete; caudal scaled for at least one-third of its length; 

 maxillary with teeth along nearly the entire anterior edge; gill-rakers long, setiform; 

 gill-membranes free from each other and from the isthmus. 



Key to the Speojes of Pristella. 

 a. Depth 2.3-2.75; A. 20-24; dorsal, anal, and very frequently ventral, each with a conspicuous black spot ; 



no caudal spot riddlei. 



aa. Depth 3.5; A. 16-18; caudal with a spot on the base of its middle rays, other fins all plain aubynei. 



187. Pristella. riddlei (Meek). (Plate XLV, fig. 3.) 

 Holopristes riddlei Meek, Proc. U. S. Nat. Mus., XXIII, 1907, 11 (Los Castillas, 



Venezuela). — Eigenmann, Repts. Princeton Univ. Exp. Patagonia, III, 1910, 



437. 



Fifty-six specimens, 12-29 mm. Wismar. (C. M. Cat. No. 1307a-j; I. TJ. 

 Cat. No. 11798.) 



Eight specimens, 37-47 mm. Georgetown trenches. (C. M. Cat. No. 

 1308a-o; I. U. Cat. No. 11800.) 



Two hundred and thirty-three specimens, 26-45 mm. Botanic Garden, 

 Georgetown. (C. M. Cat. No. 1309a-z; I. U. Cat. No. 11796.) 



Five specimens, Christianburg Canal. (C. M. Cat. No. 1310a; I. U. Cat. 

 No. 11799.) 



Three specimens, Kumaka, Demerara River. (C. M. Cat. No. 1311a; I. U. 

 Cat, No. 11797.) 



Head 3.75-4; depth about 2.3-2.75; D. 11 ; A. 20-24; scales 5-32-3, six to eight 

 with pores; eye 2.64, snout 4.12, interorbital about 2.5 in the head. 



A humeral spot over the third and fourth scales of the lateral line; no caudal 

 spot; dorsal, anal, and ventrals each with a conspicuous, jet-black spot; dorsal spot 

 not extending upon the last ray, and leaving base and tips of rays hyaline; anal 

 spot covering the third and fourth fifth of the rays forming the anterior lobe ; ven- 

 tral spot leaving the outer and inner rays and bases and tips of all the rays hyaline. 

 Very brilliant in life, translucent, the caudal bright red, upper parts tinged with 

 red, basal part of dorsal and anal lobe below the black spots bright yellow, the 

 distal parts milk-white. 



188. Pristella aubynei Eigenmann. (Plate XLV, fig. 4.) 

 Pristella aubynei Eigenmann, Ann. Carnegie Mus., VI, 1909, 24; Repts. Princeton 

 Univ. Exp. Patagonia, III, 1910, 437. 



