642 Sexual Differences in Poiciliid Fishes, 



longitudinal series. Similar to C. bellottii in form and 

 coloration in both sexes ; back in front of dorsal fin arched, 

 bearing a series of bony tubercles; head bony, with post- 

 orbital tubercles. 



Province of Buenos Aires. 



Total length 85 mm. 



2. Cynolebias holmbergi. 

 Berg, t c. p. 296. 



c?. D. 21, A. 25 ; ? . D. 17, A. 21. At least 60 scales 

 in a longitudinal series. Head 3^ to 3^ in length to base of 

 caudal. Yellowish ; a dark bar on the head. 



Province of Buenos Aires. 



Total length 300 mm. 



In C. melanoicenia the males are similar to the females both 

 in coloration and in number of fin-rays ; in this species the 

 pelvic fins are separated by an interspace, whereas in Cyno- 

 lebias proper they are contiguous and often united at the 

 base. I therefore propose to make C. melanotienia the type 

 of a new genus, which may be named Cynopcecilus. 



I have ascertained that the types of C. robustus and 

 C. niyripinnis are males ; the single example of C. elungatus 

 in the British Museum collection has been evisceiated, but 

 it seems probable that the two or tliree specimens known of 

 this species are females, whilst the type of C. porusus may be 

 a female also. 



Assuming this to be the case, the number of scales in a 

 longitudinal series, and of dorsal and anal rays in bothsexes^ 

 of the species of Cynolebias may be tabulated as follows : — 



