314 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. X. 



fin of the males. Since, with two exceptions, all the species treated of 

 here belong to this subfamily, we have followed for the most part 

 Mr. Regan's classification. However, in as much as the modified anal 

 fin of the males vary so essentially in different species, its use as a generic 

 character seems to us to lead to too many divisions, resulting in nearly 

 as many genera as species. It is, therefore, our opinion that this char- 

 acter should be regarded of specific, rather than of generic importance. 



KEY TO THE GENERA. 



a. Males with the anal fin advanced and modified into an intro- 

 mittent organ. Species viviparous. 



b. Ventral fins similar in both sexes. 



c. Mouth not wholly transverse, the cleft partly lateral; teeth 

 conical, immovable. 



d. Distal portion of produced rays of anal fin in male directed back- 

 ward, usually with one or more retrorse spines or hooks. 



Gambusia, p. 314. 



dd. Distal portion of produced rays of anal in male directed forward, 

 with or without antrorse hooks. Priapichthys, p. 319. 



cc. Mouth transverse; teeth slightly compressed, movable; the 

 intromittent organ long and slender, without hooks or serrations 

 at apex. Pceciliopsis, p. 324. 



bb. Ventral fins in the male enlarged, the second ray notably pro- 

 duced; teeth in the jaws movable; the first prolonged ray of anal 

 fin in male bearing a small antrorse hook at apex. 



Mollienisia, p. 326. 



aa. Anal fin in the males not modified into an intromittent organ. 

 Species viviparous. Rivulus, p. 330. 



38. Genus Gambusia Poey. 



Gambusia Poey, Memorias, I, 1855, 382 (type Gambusia punctata Poey). 

 Gambusia Regan, Proc. Zool. Soc. Lond., 1913, 981. 



Body elongate, moderately compressed in the female; mouth small, 

 the branches of the lower jaw firmly united; teeth fixed, conical, in 

 bands, the outer ones slightly the larger; branchiostegals 6; anal fin of 

 female more or less in advance of the dorsal; anal of male much ad- 

 vanced, its anterior rays modified into an intromittent organ; alimentary 

 canal short; vertebrae about 32; viviparous. 



This genus, as restricted by Regan, includes species in which the 

 modified anal of the male is about ^ the length of the body of the fish 

 and is formed of three rays. 



