Sexual Differences in PoecUiid Fishes, 641 



LXXXII. — Sexual Differences in the Pa'ciliid Fishes of the 

 Genus Cyiiolebias. By C. Tate IIegan, M.A. 



(Published by permission 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 

 preparii^g my revision of the genus Cynolebias ('Annals/ 

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

 the description of two new species, but for the conclusion 

 that Cynolebias bellotlii is the male and C. maculalus 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 iu 

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

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

 iu support of this. After examination of the sexual organs 

 of all the specimens of Cynolebias in the collection of the 

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

 but I am not acquainted with any other instance iu 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. 



Brownish, sometimes with ver- 

 tical series of pale spots ; fius 

 violet. 



Dorsal and anal fins relatively 

 long, low, and niauy-rayed. 



1). 21-24, A. 26-yl : dorsal origin 

 equidistant from end of suout and 

 base of caudal fin, behind that of 

 anal ; longest rays ^ to § length of 

 head. 



In consequence of the length of 

 the anal the pectoral extends be- 

 yond its origin and the caudal 

 peduncle is shorter than deep. 



$ C. maculatus. 



Vertically expanded dark brown 

 or violet spots on body and vertical 

 fins. 



Dorsal and anal fins relatively 

 short, deep, and few-rayed. 



D. 10-19, A. 22-26: dorsal origin 

 nearer to base of caudal than to 

 end of snout, above that of anal ; 

 longest rays | or | length of head. 



The pectoral does not reach the 

 anal and the caudal peduncle is 

 longer than deep. 



Similar differences are exhibited by the two species 

 described by Berg ; these are : — 



1 . Cynolebias yibberosus. 

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



<S . D. 25, A. 33; ? . D. 17, A. .26. 37 to 40 scales iu a 



