F^IGENMANN : THE EXPEDITION TO BRITISH GUIANA. 17 



marginal grooves; frontal fontanel shorter, triangular; second sub- 

 orbital covering the entire cheek with the exception of a triangular 

 area below the junction between the first and second suborbital ; 

 maxillary much shorter than the eye, 3 in the head ; four or five teeth 

 in the first row of the premaxillary, if five, the third very slightly out 

 of line with the others ; five graduated teeth in the second row, their 

 denticles arranged in a slight crescent ; four to seven teeth in the 

 maxillary ; mandible with four large teeth, abruptly smaller ones on 

 the sides. 



Scales everywhere regularly imbricate, no omitted or interpolated 

 scales ; each scale of the side with from two to eight diverging striae ; 

 anal sheath of very few scales in a single series along the base of the 

 anterior rays ; a few scales on the base of the caudal lobes. 



Ventrals slightly nearer snout than the dorsal ; the origin of the 

 dorsal in advance of the middle, its highest ray 3.25 in the length ; 

 anal deeply emarginate, the second and eleventh reaching the base of 

 the eighteenth ; ventrals reaching anal, pectorals slightly beyond 

 ventrals. 



Opercle dusky ; a dark vertical band crossing the third to the sixth 



scales behind the head ; a dusky streak below origin of dorsal ; sides 



behind this profusely dotted; margins of scales of the sides of the 



abdomen with a few color-cells ; very few cells on the cheeks ; base 



and tip of dorsal hyaline, the middle with chromatophores ; adipose 



dotted ; caudal nearly uniformly dotted, a small area at base of each 



lobe free from chromatophores ; anal lobe and a streak through its 



middle free from pigment ; ventrals and pectorals practically free from 



pigment. 



Astyanax essequibensis sp. nov. 



Type, 53 mm. (No. 1018 Carnegie Museum Catalog of Fishes.) 

 Tumatumari, Potaro River. 



Cotypes, 96 specimens, 40-68 mm. Tumatumari, Potaro River. 

 (C. M. Cat. No. 1019, a-z; I. U. Cat. No. 11721.) 



Cotype, 1 specimen, 44 mm. Bartica, Essequibo River. (C. M. 

 Cat. No. 1020.) 



Cotypes, 3 specimens, 41-48 mm. Rockstone, Essequibo River. 

 (C. M. Cat. No. 1021, a; I. U. Cat. No. 11722.) 



Cotypes, 75 specimens, 39-57 mm. Crab Falls, Essequibo River. 

 (C. M. Cat. No. 1022, a-z; I. U. Cat. No. n 723.) 



Allied to paucidens, but having a well-developed humeral spot. 



