6 Carl L. Hubbs 



II 

 The gonopodium is the chief distinctive feature of the Poecihidae (as 

 here dehmited). In the other groups of viviparous cyprinodonts the anal 

 fin, to be sure, is also modified as an intromittent organ, but in so different 

 a fashion as to indicate an entirely independent origin as compared with the 

 gonopodium. It is highly probable that the Goodeidae, Poeciliidae and Ana- 

 blepidae, as well as the remarkable Phallostethidae of the Malay Peninsula, 

 originated independently from the oviparous Cyprinodontidae.'* It is, there- 

 fore, probable that viviparity has been independently acquired four times 

 among the cyprinodont fishes. If this view is correct, we have in the present 

 case a most striking example of the independent attainment, within one 

 group of animals, of one end through diverse adaptation. The oviparous 

 Cyprinodontidae, it would further follow, have had and probably still possess 

 the potentiality of developing viviparity. In fact, many of the species of 

 this family show an approach toward the viviparous condition in the develop- 

 ment of clasping structures and habits.^ 



In the following key to the genera of the Poeciliidae the family is divided 

 into four subfamilies, — the Gambusiinae, Poeciliopsinae, Poeciliinae and 

 Tomeurinae. These groups are of unequal size, but are recognized as co5r- 

 dinate because each appears to have evolved from the basal stock of the 

 whole family, each being characterized by certain primitive as well as special- 

 ized features. Of the four subfamilies, the Gambusiinae are without ques- 

 tion the least specialized, while Tom^urus is the most highly modified poeciliid. 

 Within these subfamilies certain clusters of genera may be recognized, 

 by reason of the remarkable coordination which they display between geo- 

 graphical distribution and gonopodial structure, as distinct groups of inde- 

 pendent origin. As it is planned to return later to a fuller consideration of 

 these phenomena, it seems desirable to assign definite names to these groups. 

 For this purpose the term tribe (with the ending -ini) may be borrowed from 

 entomology. 



in 

 In the key one new subfamily, nine new tribes, nine new genera, and one 

 new species are diagnosed. A list of these new names follows: 

 New subfamily name: Poeciliopsinae. 



New tribe names: Gambusiini, Xiphophorini, 



Heterandriini, Poeciliini, 



Girardinini, Alfarini, 



Cnesterodontini, Tomeurini. 



Pamphoriini, 

 New genera: Panamichthys, Xenophallus, 



Allogambusia, Neopoecilia, 



Darienichthys, Parapoecilia, 



AUoheterandria, Allopoecilia. 



Phallichthys, 

 New species : Neopoecilia holacanthus. 



4 The major classification of the cyprinodont fishes is considered in the preceding 

 paper of this series. 



5 See Newman, Biol. Bull., 12, 1907, pp. 314-348, 3 pls. and 22 figs. 



