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 Comparative 

 Zoology, 1911. 



Key to the Guiana Species (if 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 by yellow in front ; A. 25 or 26; scales 5-30 



or 31—4 oligolepis. 



bb. 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. Eye 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. Striae 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 yellowish in life; A. 26-30; scales 7-33 or 34-5. 



chrysargyrea. 

 //. 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 ; three 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. 



hit. 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 1 lepidura. 



ii. Caudal lobes alike. 



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



5-32-3 to 5 cotinho. 



jj. Caudal plain. 



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



kk. Anal rays 1S-20; upper caudal lobe rose-colored or rusty; anal and dorsal with yellow; 

 scales 5-32 to 34-3.5 copei. 



175. Mcenkhausia oligolepis (Gunther). (Plate XLVI, fig. 3.) 

 Tetragonopterus tamiatus (not of Jenyns) Muller and Troschel, in Schomburgk, 



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

 Tetragonopterus oligolepis Gunther, 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). 



