71 



The cliaracteristics of the fish-fauna of Eastern Xearctica are much 

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

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

 Percidae, embracing many species, known as Utheostominae, have the 

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

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

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

 ing rivers and streains 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 Eocky Mountains; and the Eocky Mountain 

 region itself, w^hich extends to the Sierra Nevada. The former is covered 

 with grass, and is almost totally treeless; the latter is covered with "sage- 

 brush" [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- 

 tilocapra,Haplocerus, and Ovis, as well as certain species of the same group, 

 i. e., Caria'cus macrotis (black-tailed deer) and C. leucurus. Other genera 

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

 SpermopMltis, Blpodomys, Perognathus, and Lagomys. A few species 

 of Spermopliilus extend into the northwestern portion of the Eastern ; 

 while the extensive genus Geomys (the subterranean gophers) range 

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

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

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



Oroscoptes. 



Hydrobata. 



Myiadestes. 



Neocorys. 



Salpinctes. 



Picicorvus. 



Chondestes. 



Valamospiza. 



Emhernagra. 



Centrocercus. 



Pedioecetes. 



'Excepting the coui«e of the Mississippi, and perhaps the Rio Grande. 



