96 Annals of the Carnegie Museum. 



above by the premaxillaries only, the mesethmoid is unpaired, and 

 all or most of the ribs are inserted on strong transverse processes. 

 Whereas the Haplomi show relationship to the more generalized iso- 

 spondylous fishes, the Microcyprini bear more resemblance to the Sal- 

 mopercae and Synentognathi, especially the latter." 



In the Oligocene and Miocene of Europe occur the fossil remains of 

 Prolebias, a generalized form, related to the recent genus Fundidus. 

 From this central type adaptive radiation has taken place, resulting 

 in considerable modification of the form of the body and structure. 

 Differences in the character of the teeth and the length of the ali- 

 mentary tract have arisen in the same subfamily through adaptation 

 to a carnivorous or a vegetable diet. In some cases evolution in one 

 species has paralleled that in another, unrelated species. For instance, 

 the ventrals have been lost in Orestias and Empetrichthys. 



The family consists of oviparous forms, in which the eggs are de- 

 posited in the usual manner, and viviparous forms, in which the ova 

 undergo development within the ovarial sack and the young are born 

 in a more or less advanced stage of development. The oviparous 

 species are contained in three sub-families, the Cyprinodontinae, 

 Orestiinae, and Fundulinse, in which the sexes do not greatly differ 

 from each other. 



Of viviparous forms there are five subfamilies. In these fertilization 

 of the female is effected, with but one exception, with the aid of the 

 anal fin, which is modified to serve as a so-called intromittent organ. 

 In the FitzroyiincE or JenynsiincB, and the Anablepince, both of which 

 are monogeneric and contain but few species, the anal rays are rolled 

 up into a tube. The Characodontincc resemble the oviparous Fiindu- 

 lincE in appearance, but the male has the first five or six rays of the 

 anal short and stiff and separated by a notch from the rest of the fin. 

 This subfamily, with the exception of a few species, is found only in 

 the basin of the Rio Lerma of Mexico. This type of anal structure is 

 much more simple than that in the Pa'ciliincE, in which the anterior 

 rays are thickened and lengthened to form a lever. 



The viviparous forms were thought to be entirely confined to the 

 western hemisphere. Quite recently Regan (b. 1913) has described 

 Phallostethus duncken, a remarkable new Poeciliid and the type of a 

 new subfamily. This fish, which ie from Johore on the Malay Penin- 

 sula, is viviparous. While in all I lie other viviparous forms, which 



