Geographic and Geologic Relations 425 



extreme specialization over that region, are slightly added 

 proofs that the family was ancestral to the latter area. 



Probably no family of the Teleostei appears more puzzl- 

 ing from the geographic and geologic standpoints than the 

 Cyprinodontidae. For though including only about 200 

 species that are typically freshwater, or that rarely become 

 brakish-water or semi-marine in habitat, the distribution 

 over tropical and warm-temperate land-areas of the world 

 is now extensive. Two genera Prolebias and Pachylebias 

 are known in about 10 species from Lower Oligocene up to 

 Upper Miocene strata of freshwater character over central 

 and south Europe. This might seem to favor origin for 

 the group there. Cope's doubtful genera Gephyrtira and 

 Proballostomus from Tertiary rocks of South Dakota need 

 not now be considered. 



Three genera Fiinduhis (including Haplochilus) with 

 about 54 species, Cyprinodon with 12 species, and Gerardi- 

 nus with 10, stand out conspicuously from the other genera, 

 alike from abundance of species, from wide distribution, 

 and from their close structural relation to fossil forms. 

 The first of these is "the most primitive and the least 

 specialized" (257:631). About 32 of its species are dis- 

 tributed from Nebraska, Missouri and New York south- 

 ward to Costa Rica, Texas, Florida and Jamaica in N. 

 America, 7 are native from Guatemala to East Brazil in 

 S. America, while the remaining 14 extend from West 

 Africa to Japan. 



But before treating of the extra-american, some atten- 

 tion should be given to the remaining genera of the family, 

 which are nearly all found from Central to S. America, and 

 amount to about 15. The presence of species in the south- 

 ern coastal states, in Cuba, San Domingo, Barbadoes, Trini- 

 dad, Martinique, Mexico, Honduras, Panama, Guatemala, 

 Venezuela, Brazil, and southward to Monte Video, fur- 

 nishes almost conclusive proof that northern S. America 

 was the centre for evolution of the family. 



The genus Orestias is of exceptional interest, for the 

 ID known species are only found in Lake Titicaca and a 

 neighboring lake, so at an elevation in the Andes of more 

 than 12,000 feet. It represents a degenerate evolutionary 



