CHARACID FISHES — ^WEITZMAN 



25 



capable, to a greater or lesser degi*ee, of twisting the anal fin into a cup- 

 shaped organ that is placed with the concave side almost over the fe- 

 male's vent during the act of laying an egg. Wickler (1957) has re- 

 corded some of the behavior of various species of nannostominans but 

 has not noted the precise use of the anal fins. Although I have not 

 seen the anal fin of the male Nannosiomus digrammus in use, its morph- 

 ology indicates that it undoubtedly changes greatly in shape during 

 the spawning act. 



Figure 6. — Anal fin of male Nannostomus digrammus, SL 19.6 mm., SU S02S1. 



Radial gi^ooves of scales belonging to third horizontal scale series and 

 lying below dorsal fin shown m figure 5. Posterior field with 1 or 2 

 radial grooves; dorsal and ventral fields each with 1 and anterior field 

 with 3 or 4 radial grooves. Scales in lateral series 25 to 26; no per- 

 forated lateral-line scales; scales in median series anterior to dorsal fin 

 10 to 11. Total number of vertebrae 34 to 35, 18 to 19 precaudals and 

 15 to 16 caudals, but always in a combination to produce a total count 

 of 34 to 35 vertebrae. 



Color in alcohol. — Top of head black. Primary horizontal stripe 

 black, extending from snout tip and lower jaw onto anterior surface 

 of eye, then from posterior surface of eye across lower border of fifth 

 orbital bone and upper border of fourth orbital, then continuing over 

 upper arm of preopercle onto opercle ending at about posterior bony 



