UNIVERSITY OF COLORADO STUDIES 

 TABLE X—Conlinuei 



1= native. 

 i= introduced. 

 ?=doubt£ul. 



River drainage. So closely related are the Rio Grande and Colorado 

 River Trout that their identity has more than once been suggested, 

 and both Pantosteus and Richardsonius are western genera whose 

 species are for the most part native to the Rocky Mountain region or 

 the Great Basin. The remaining native species of the Rio Grande in 

 Colorado is the Green Sunfish, Lepomis cyanellus, a fish of eastern 

 relationships. The Centrarchids are among the most characteristic 

 fishes of the Mississippi Valley, so that Lepomis cyanellus is to be 

 regarded as an immigrant from the East. With four of the five native 

 species of the Rio Grande in Colorado western forms, the fish fauna 

 of that drainage is more closely related to the fish fauna of the Colorado 

 River than to that of the Mississippi Valley. 



The small niimber of native species in the Rio Grande in Colorado 

 may be the result of several limiting conditions, but from a com- 

 parison with the number of species of other drainages at the same 

 altitude it seems that altitude is perhaps the important factor in this 

 connection. 



