No. 6. — Zoological fiesults of the Thayer Brazilian Expedition. 

 Preliminary descriptions of Neiv Genera and Species of Tetra- 

 gonopterid Characins. 1 



By Carl H. Eigenmann. 



The following species, mostly collected during the Thayer Expedition, 

 will be fully described and figured in a monograph of the Characidae to 

 appear in the Memoirs of the Museum of Comparative Zoology. 



The monograph will be issued at irregular intervals, and the account 

 of the Tetragonopterinae, which forms the first section of the systematic 

 part of the monograph, will be delayed on account of the desirability of 

 securing material from some of the South American rivers flowing north 

 into the Caribbean. 



Gymnocorymbus, gen. nov. 



Resembling Moenkliausia, from which it differs in the naked predorsal line. 

 Type. — Gymnocorymbus thayeri, sp. nov. 2 



Gymnocorymbus thayeri, sp. nov. 



Head 3.5 (average) ; depth 1.7 (average) ; D. 11 ; A. 34-41, usually 37 

 or 38. 



Very deep and very much compressed ; the ventral outline much greater than 

 the dorsal, pendant, deepest at origin of aual. 



Snout very short, mouth very oblique. 



Scales cycloid, regularly imbricate. 



Color similar to that of Tetragonopterus argenteus. A dark humeral bar fol- 

 lowed by a lighter area, and this again by a bar less well-marked than the first ; 

 area between the two bars, just above lateral line, bright silvery. Lower sides 

 brassy ; fins hyaline to uniform dusky. 



Males with hooklets on aual. 



1 Contributions from the Zoological Laboratory of Indiana University, No. 99. 



2 In memory of S. V. R. Thayer, a volunteer of the Thayer Expedition. 



