ElGENMANN : THE EXPEDITION TO BRITISH GUIANA. 41 



Pectorals reaching ventrals or not, the tips of the outer rays not 

 thickened ; ventrals not to anal ; anal rounded, the fifth ray highest, 

 reaching slightly beyond tip of last, not nearly to caudal ; dorsal low, 

 subtruncate, the third ray not quite reaching tip of last ; base of dorsal 

 extending halfway to tip of adipose, 7.75 in the length. 



Pellucid in life. Sides of head and body more or less iridescent ; 

 a dark stripe from eye to end of snout ; about ten dark brown cross- 

 bars, most intense on back and along the lateral line; the centers of 

 the scales of the bars colorless, giving each band a chain-like appear- 

 ance ; a few chromatophores on the margins of other dorsal scales. A 

 minute, round black spot at base of caudal, surrounded by a hyaline 

 area, which is bounded posteriorly by a faint color halo ; fins other- 

 wise all hyaline. A blackish median line from behind ventrals to the 



vent. 



Nannostomus marginatum sp. nov. 



Type, 26 mm. (No. 11 71 Carnegie Museum Catalog of Fishes.) 

 Maduni Creek. 



Cotypes, 10 specimens, 21-25 mm. Maduni Creek. (C. M. Cat. 

 No. 1 172, a-d ; I. U. Cat. No. 11 696.) 



Cotypes, 5 specimens, 19-24 mm. Lama Stop-Off. (C. M. Cat. 

 No. 1173, a > &> I- U. Cat. No. 11697.) 



Cotypes, 2 specimens, 22, 23 mm. Crab Falls. (C. M. Cat. No. 

 1174,0; I. U. Cat. No. 11698.) 



Cotypes, 2 specimens, 24 mm. Rockstone sand bank. (C. M. 

 Cat. No. 1 175, a ; I. U. Cat. No. 11699.) 



Cotypes, 5 specimens, 25-31 mm. Gluck Island. (C. M. Cat. No. 

 1176,0, b ; I. U. Cat. No. n 700.) 



Cotypes, 2 specimens, 27, 31 mm. Christianburg canal? (C. M. 

 Cat. No. 1 1 77, a ; I. U. Cat. No. 11 701.) 



Cotypes, 19 specimens, 21, 22 mm. Cane Grove Corner. (C. M. 

 Cat. No. 1 1 78, a-f; I. U. Cat. No. 11 702.) 



Most nearly related to N. trifasciatus Steindachner. 



Head 3.6 ; depth 3.4 ; D. 10 ; A. 11 or 12 ; scales, 5 between D. 

 and V., 9 or 10 before the dorsal, 21 in a median lateral series. Eye 

 3 in the head ; snout 4 in the head ; interorbital equal to the eye. 



Short and chubby, the snout especially short, the jaws equal. 

 Origin of the dorsal over the insertion of the ventrals ; pectorals 

 reaching a little more than half way to the ventrals ; ventrals half way 

 to middle of anal. No adipose fin. 



