71 



The cbaracteristics of the fish-fauna of Eastern Nearctica are much 

 more marked; two entire orders, represented by the gar {Oinglymodi) 

 aud dog-fish {HaleconwrpM), are confined to it, and a series of genera of 

 Percidae, embraciDg many species, known as Etheostominae, have the 

 same range. The Siluridae all belong here, as well as a great majority 

 ot the genera of Cyprinidae and Catostomidae. In all of these divisions, 

 the region is very rich in species, owing to the abundance of everflow- 

 iug rivers and streams which drain it. The Polyodontidae (spoon-bill or 

 paddle-fish) are not found in any of the other regions.* 



The Central region is characterized by the general absence of forests, 

 as compared with the Eastern. It presents two distinct divisions, each 

 peculiar in its vegetation : the division of the plains, which extends from 

 the eastern border to the Rocky Mountains; and the Eocky Mountain 

 region itself, which extends to the Sierra Nevada. The former is covered 

 with grass, and is almost totally treeless ; the latter is covered with ^^sagc- 

 hvnsih'^ {Artemisia), a short stout bush, which forms extensive areasof tree- 

 less brush. The grass-covered plains are the range of the bison, though it 

 formerly sought also the tracts of grass occasionally found among the 

 Artemisia. The region, as a whole, is distinguished from the Eastern 

 by the possession of several genera of ruminating Artiodactyles, i. e.. An- 

 tHocapra,Ha2)locerns, and Om, as well as certain species of the same group, 

 i, €., Cariacus macrotis (black-tailed deer) and C. leucurus. Other genera 

 of mammals which distinguish it from the Eastern are Taxidea, Cynomys, 

 Spcrmopliilus, Dipodomys, PerognatJms, and Lagomys. A few species 

 oi Spermophilus extend into the northwestern iiortion of the Eastern; 

 while the extensive genus Geomys (the subterranean gophers) range 

 over the Central subregion, aud into the Western aud Gulf States 

 the Austroriparian as far as the Savannah River. A great many species 

 of birds are peculiiir to the Central region, and the following genera : 



Oroscoptes. 



Ilydrohata. 



Myiadestes. 



Keocorys. 



Salpinctes. 



Picicorvus. 



Chondestcs. 



(Jalamospiza, 



Ember nagra. 



Ccntrocercus. 



Pedioecetes. 



* Excepting the coni'se of the Mississippi, and porliaps tho Rio Giaiulti. 



