EIGENMANN: the freshwater fishes of BRITISH GUIANA 487 



Head 2.75; depth 2.33; D. XVI,7; A. 111,7; scales 23 along a median series; 

 lateral line 15 or 16 + 16 to 18; upper lateral line scarcely interrupted; eye 3.33 

 in the head, 1 in the interorbital; snout but little shorter than the eye. 



Maxillary extending to below anterior margin of the eye; one-fourth of the 

 eye in the posterior half of the head; about five gill-rakers. Teeth in two or three 

 series, those of the outer row much the larger. Second scale of the lateral line 

 separated by five scales from the dorsal, the fifth to the tenth by one and one-half 

 scales, the last scale of the upper lateral line by half a scale. 



A dark band from below the middle of the eye to the angle of the preopercle. 

 Sides with about six cross-shades, the middle one with a distinct spot below the 

 lateral line. A small round black spot above the last scale of the lateral line. 



iEquiDENS*- Eigenmann and Bray. 

 Acara, part, Heckel, Ann. Wiener Mus., II, 1840, 338. 

 j^quidens Eigenmann and Bray, Ann. N. Y. Acad. Sci., VII, 1894, 616. 



Type, Acara tetramerus Heckel. 



Gills with minute rakers and no lobe; mouth small, not greatly protractile. 

 Anal with three spines; lateral line well separated from the dorsal; soft fins naked, 

 or with scales at their bases only, preopercle entire; scales of the lateral line of 

 the same size as those above and below it. 



Key to the Guiana Species of ^Equidens. 

 a. Oval or suhrhomboidal, the ventral i^rofile equally arched with the dorsal; lateral line not forked on the 

 caudal; caudal peduncle shorter than deep; caudal rounded. 

 b. Dorsal and anal densely scaled at the base; preopercle scaled. Caudal peduncle one-fourth to one- 

 third as long as deep; an ocellated spot above the posterior part of the lateral line.. . .maronii. 

 66. Dorsal and anal naked, except sometimes a scale at the base of the membranes. Preopercle naked, 

 c. A dark band from the eye to the base of the hinder dorsal rays; a black spot below the middle of 

 the upper lateral line and another at the base of the upper caudal rays; soft dorsal and anal 

 in the adult sometimes with a single scale on the membranes; caudal peduncle two-thirds 



or three-fourths as long as deep vittatus. 



cc. A black band from the eye to the spot at the base of the upper caudal rays. 



d. A dark band from the eye down to the preopercle potaroensis. 



dd. A dark spot below and behind the eye tetramerus. 



aa. Dorsal profile much more greatly arched than the ventral; lateral line forked on the caudal; caudal iseduncle 

 as long as deep; dorsal and anal naked; caudal cniarginate; eye entirely in the jiosterior half of the head 

 in the adult; preorbital very deej). A black bar from the nape through the eye to the angle of the pre- 

 opercle; a dark band from the eighth dorsal spine to in front of the anus geayi. 



'- The reasons for using Jiquidens are given at length in Reports Princeton Univ. Exp. Patagonia, III, 

 1910, 470. 



