ElGENMANN \ THE EXPEDITION TO BRITISH GUIANA. 33 



emarginate ; ventrals reaching anal, pectorals to ventrals, or but a 

 trifle shorter. 



Hyaline ; a conspicuous silvery lateral band ; sides of head silvery ; 

 a vertical humeral spot crossing the second scale of the lateral line ; 

 three parallel dark lines along the middle of the back ; scales of the 

 back margined with several rows of chromatophores ; chromatophores 

 along base of anal and scattering ones on the sides, a band of chro- 

 matophores below the silvery baud ; a narrow dark band from the tip 

 of the first (short) dorsal ray to the tip of the penultimate, tips of the 

 longer rays and bases of all the rays hyaline ; caudal everywhere punc- 

 tate, except at the tips of the rays and a triangular patch adjoining 

 the middle rays above and below, these parts hyaline ; tips of highest 

 anal rays milky ; tips of the other rays dark, the dark continued across 

 the longest rays at the same level ; pectorals and ventrals more or less 



dotted. 



Holobrycon gen. no v. 



Type : Brycon pesu Miiller & Troschel. 

 This genus is a Brycon without fontanels. 



Brycon pesu was collected at all stations between Bartica and Tuma- 

 tumari. 



Triurobrycon gen. no v. 



Type : Brycon lundii Liitken. 



This genus is distinguished from Brycon by the elongation of the 

 middle caudal rays into a point. 



Subfamily CrenuchiNtE. 



The Crenuchinse are Aphiocharacinae with an increased number of 

 dorsal rays. They resemble some of the genera of Pceciliidae. 



But a single species has been recorded, Crenuchus spilurus Gunther, 

 from the Amazon and the Guiana lowlands. 



I found a second species representing a second genus very abundant 

 on the Guiana plateau and just below the Kaieteur Fall. 



The genera are distinguished by the following characters : 



a. An adipose fin; mouth large, maxillary extending to below middle of eye. 



Crenuchtis Gunther. 



aa. No adipose fin ; mouth small, maxillary extending to below anterior margin 



of eye. Pxcilocharax Eigenmanm 



