DISPERSION OF FRESH-WATER FISHES. 101 
this is perhaps a returned emigrant from America, 
rather than a direct offshoot of the parent stock. 
The Suckers are modified Cyprinidae, 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 Cyprinide 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, Votropis, 
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 Cichlids, —a group especially characteristic of 
tropical America, one species of which reaches 
southern Texas. 
The Moon-eyes are characteristically American 
type, with no near relatives elsewhere in the world. 
Their ancestors were probably immigrants from 
the sea. 
The Herring permanently resident in our fresh 
waters are simply landlocked representatives of 
