Sexual Differences in PcecUiid Fishes. 641 



LXXXII. — Sextial Differences in the Pocciliid Fishes of the 

 Genus Cynolebias. By C. Tate Regan, M.A. 



(Published by permissiou of the Trustees of the British Museum.) 



Herr a. Rachow, of Hamburg, has written calling my 

 attention to the fact that I have overlooked a paper by 

 C. Berg (Anales Mus. Nac. Buenos Aires, v. 1897) when 

 preparing my revision of the genus Cynulebias (* Annals,' 

 Nov. 1912, p. 505). Berg^s paper is important not only for 

 the description of two new species, but for the conclusion 

 that Cynoltbias bellottii is the male and C. maculatus the 

 female of one species, the difference in the number of dorsal 

 and anal rays being a sexual character. 



Herr Rachow tells me that from his own observations in 

 the aquarium there can be no doubt that C. maculatus is the 

 female of C. bellottii, and he has sent me some specimens 

 in support of this. After examination of the sexual organs 

 of all the specimens of Cijnolebias in ihe collection of the 

 British Museum, 1 have no doubt whatever that he is right ; 

 but I am not acquainted with any other instance in the 

 whole class of fishes of a difference between the sexes in the 

 number of fin-rays. 



The males and females of C. bellottii differ as follows : — 



(S C. bellottii. : 5 C. maculatus. 



Brownish, sometimes with ver- i Vertically expanded dark brown 



tical series of pale spots ; fins or violet spots on body and \ ertical 



violet. I fins. 



Dorsal and anal fins relatively ' Dorsal and anal fins relatively 



long, low, and manv-raved. ' short, deep, and few-raved. 



D. •2\-24r, A. 26-31 : dorsal origin D. lG-19, A. ■22-26 : dorsal origin 



equidistant from end of snout and nearer to base of caudal than to 



base of caudal fin, behind that of j end of snout, above that of anal ; 



anal ; longest rays i to § length of longest rays 5 or | length of head, 



head. ' 



In consequence of the length of j The pectoral does not reach the 



tlie anal the pectoral extends be- : anal and the caudal peduncle is 



youd its origin and the caudal longer than deep. 

 peduncle is shorter than deep. 



Similar differences are exhibited by the two species 

 described by Berg ; these are : — 



1 . Cynolebias gibberosus. 

 Berg, Anales Mus. Xac. Buenos Aires, v. 1897, p. 294. 

 ^ . D. 25, A. 33; ? . D. 17, A. 26. 37 to 40 scales in a 



