Mammals of the Boreal Region. 23 



Allo^lianies, a ('(Mitral arm in the Rocky Mountains, and a west- 

 ern arm in the Cascades and Sierra Nevada. The latter at its 

 northern base occupies the entire breadth of the Pacific Coast 

 region from the eastern slope of the mountains to the sea, but in 

 passing southward bifurcates, the main fork following the lofty 

 Cascade and Sierra ranges to about latitude 36 ; the other fol- 

 lowing the coast, gradually losing its distinctive characters and 

 becoming invaded with Sonoran forms until it disappears a little 

 north of San Francisco. 



The following genera of mammals belong exclusively to the 

 Boreal Region, none of them ranging south beyond the Transi- 

 tion Zone : 



Cervus Cuniculus 



Rangifer Zapus 



Alee Erethizon 



Mazama Lagomys 



Ovibos Thalarctos 



Arctomys Latax 



Aplodontia Gulo 



Evotomys Mustela 



Phenacomys Neurotrichus (?) 



Myodes Condylura 



In addition to the above, the following genera are clearly of 

 Boreal origin, although reaching and in some cases penetrating 

 parts of the Sonoran Region : 



Ovis Vulpes 



Bison * Ursns 



Tamias Lutreola 



Castor Putorius 



Arvicola Sorex 

 Fiber 



Besides the genera here enumerated, the following subgenera 

 belong to the Boreal Region : Tamiasciurus (containing the red or 

 spruce squirrels), Mynomes and Chilotus (field-mice or voles, of 

 which Mynomes reaches south a little beyond the Transition 

 Zone), Teonoma (the bushy-tailed wood-rats), and Neosorex and 

 Atophyrax (subgenera of shrews). 



* The fkunal position of the genus Bison is not so certain as in the case 

 of the other genera here mentioned, though both the American and the 

 European species seem to be of Boreal origin. 



