DISPERSION OF FRESH-WATER FISHES. 1 01 



this is perhaps a returned emigrant from America, 

 rather than a direct offshoot of the parent stock. 



The Slickers are modified Cyprmidce, probably- 

 developed originally in America, although one 

 species has spread from Alaska to Siberia, and 

 another very peculiar form exists in China. What- 

 ever its origin, this group is now one of the most 

 characteristic of our fauna. 



The Cyprinidce of western America are more or 

 less closely related to Old World types, and some 

 of them, like the Old World species, reach a great 

 size. East of the Rocky Mountains are found a 

 multitude of species, mostly of small size and 

 weak organization, which seem to be degenerate 

 or reduced representatives of Old World types, 

 and which have for the most part no immediate 

 relatives among the latter. The majority of these 

 species are now placed in a single genus, Notropis^ 

 which is found only in America, and is one of the 

 most characteristic of our fish-fauna. 



The Characins belong to the tropics, especially 

 to South America. The single species which 

 crosses the Rio Grande is doubtless an immigrant 

 from Mexico. The same remarks apply also to 

 the CicJilids, — a group especially characteristic of 

 tropical America, one species of which reaches 

 southern Texas. 



The Mooji-eyes are characteristically American 

 type, with no near relatives elsewhere in the world. 

 Their ancestors were probably immigrants from 

 the sea. 



The Herrmg permanently resident in our fresh 

 waters are simply landlocked representatives of 



