Durbin : The Expedition to British Guiana. 61 



Origin of dorsal less than half the length of the eye nearer the caudal 

 than the snout. Penultimate ray two-fifths of the longest, which is 

 three and one-fifth into the length. Origin of the anal on the vertical 

 from the first to third scale behind the dorsal. Anal deeply emargi- 

 nate, the longest ray almost equal to the base. Caudal a very little 

 longer than the head. Ventrals on the vertical from the second or 

 third scale in front of the dorsal. Ventrals just reaching the anal, 

 pectorals just barely reaching the ventrals, or more often reaching to 

 the second or third scale in front of the ventrals. 



Humeral spot conspicuous, black, vertically elongate, surrounded by 

 a small light area. Caudal spot variable in intensity, not continued 

 upon the caudal rays, and not continuous with the narrow black lateral 

 stripe, which is overlaid with silvery. Scales of the postdorsal region 

 each marked with a round dark spot in addition to a few scattered 

 chromatophores. Scales of the predorsal region with less distinct 

 round spots and a generally more pronounced dusky shading. Scales 

 of the sides above the lateral stripe outlined with dusky. A few 

 chromatophores scattered over the region between the anal and the 

 lateral stripe. There are some indications of a very faint secondary 

 humeral spot. All fins somewhat dusky. Caudal with an orange spot 

 on the base of each lobe (evident in living specimens only). 



Hemigrammus orthus sp. no v. 



Type, 28 mm. (No. 1477 Carnegie Museum Catalog Fishes.) 

 Tukeit. 



Cotypes, 17 specimens, 22-30 mm. Tukeit. (C. M. Cat. No. 

 1478, a-f; I. U. Cat. No. 11912.) 



Cotypes, 25 specimens, 14-21 mm. Gluck Island. (C. M. Cat. 

 No. 1479, a ~f) I- U. Cat. No. 1 1922.) 



Cotype, 1 specimen, 27 mm. Essequibo below Packeoo. (C. M. 

 Cat. No. 1480.) 



Distinguished by a diffuse humeral spot, and a black lateral stripe. 

 A black line at the base of the last anal rays, separate from that at the 

 base of the first seven. Dorsal, caudal, and first seven rays of the anal 

 dusky. No caudal spot. Maxillary equal to the eye. 



Head 3.75, depth 3.75 ; D. 11, A. 19 to 22 ; scales 5-30 to ^3~3 I 

 eye 2.5 in the head; interorbital not quite equal to the eye, about 

 3 in the head. 



Compressed, head at the base of the occipital process about three- 



