EIGENMANN: the freshwater fishes of BRITISH GUIANA 321 



Only outlines of the characters of the species of this genus are given. A full 

 account of all of them will appear in the Memoirs of the Museum of Com-paraiive 

 Zoology, 1911. 



Key to the Guiana Species of Mcenkhausia. 

 a. Depth 2-2.7; A. 23-30; occipital process one-third to one-fifth of the distance of its base from the dorsal. 

 b. A broad black band across the base of the caudal, bordered bj- yellow in front ; A. 25 or 26; scales 5-30 



or 31— i oligolepis. 



66. Caudal plain or with a small basal spot. 



c. Depth less than 2 in the length; A. 34; scales 7. .5-35-7 profunda. 



cc. Depth 2 or more in the length. 



d. Ej'e 2.3 or more in the head ; no caudal spots. 



e. Striae of scales diverging from the middle line of each scale in nearly opposite directions; 



depth 2 in the adult; A. 26-28; scales .5-33-4 grandisquamis. 



ee. Strife of scales parallel or but slightly diverging. 



/. A conspicuous humeral spot nearly equidistant from opercle and the vertical from the 

 dorsal ; iridescent silvery, the fins yellowi.sh in life; A. 26-30; scales 7-33 or 34-5. 



chrysargjrrea. 

 //. Humeral spot much nearer opercle than dorsal; scales of the sides with a dark margin. 



A. 23 or 24; scales 5-30 to 34-3 browni. 



dd. Eye 2-2.2 in the head. 



g. No caudal spot, a vertical humeral spot; A. 28-30; scales 5-35 or 36-4 megalops. 



gg, A median caudal spot, no humeral spot; A. 26; scales 5-34-3 or 4 shideleri. 



aa. Depth 2.75 or more in the length ; tliree or four scales (rarely five in cotinho) between lateral line and ventrals. 

 h. Caudal lobes with a median black cross-band, the base canary yellow in life, the tips white. A. 25-28; 



scales 5 or 5.5-34 to 39-3 or 3.5 dichroura. 



hh. Caudal lobes without cross-band. 



i. Upper caudal lobe black with a red or yellow spot at its base; a faint humeral spot; A. 22-27; 



scales 5-34-4 lepidura. 



ii. Caudal lobes aUke. 



j. A veiy conspicuous large black caudal spot, surrounded by rusty in life. A. 20 or 21; scales 



5-32-3 to 5 cotinho. 



jj. Caudal jjlain. 



k. Anal rays 23-24; vertical fins tinged with red; scales .5-34-3.5 colletti. 



kk. Anal rays 18-20; upper caudal lobe rose-colored or rusty; anal and dorsal with yellow; 

 scales 5-32 to 34-3.5 copei. 



175. Moenkhausia oligolepis (Giinther). (Plate XLVI, fig. 3.) 

 Tetragonopterus tceniatus (not of Jenj^ns) Muller and Troschel, in Schomburgk, 



Reisen, III, 1848, 635 (trenches and swamps along the coast). 

 Tetragonopterus oligolepis Gijnther, Catalogue, V, 1864, 327 (British Guiana). — 



EiGENMANN and EiGENMANN, Proc. U. S. Nat. Mus., XIV, 1891, 53.— Ulrey, 



Ann. N. Y. Acad. Sci., VIII, 1895, 282.— Vaillant, Bull. Mus. d'Hist. Nat., 



V, 1899, 155(Carnot). 



