THE HOLARCTIC REGION. 



[CHAP. 



Rodentia. 



Tamtas. Ranges into Sonoran. 



Arctomys. 



Spermophilus. 



CASTORID^E. Castor. *) .. 



,, ,,-. \ Also Sonoran. 



MURID^E. Microtus. } 



Myodes. 



Cuniculus. 



LA COM YIDSE. Lagomys. 



LEPORID^:. Lepus, the greater number of species Hol- 

 arctic. 



Ungulata. 



Bos, the bison group chiefly Holarctic, al- 



though the American species reaches 



the Sonoran. 

 Ovis, just touches Oriental, and also reaches 



Sonoran. 

 Ovibos, now extinct in the Old World, where 



it was common in the Plistocene. 



The arguments for the unity of the Holarctic region are, how- 

 ever, by no means confined to the case of genera, for there are a 

 number of species which either have a circumpolar range, or 

 which are represented by closely allied forms in the opposite 

 hemisphere. It is true, indeed, that many of these are now more 

 or less exclusively Arctic in their distribution, but some range a 

 long distance to the south ; while during the Plistocene epoch this 

 was the case with the majority. The following list includes the 

 more important species which are either common to the eastern 

 and western halves of the region or have representative forms 

 in the two hemispheres ; those which are strictly Arctic having 

 the letter P appended : 



1. Common lynx (Felis lynx). Canadian lynx (F. cana- 



densis). P. 



2. Wolf (Cants lupus). 



3. Fox (Cants vulpes). 



4. Arctic fox (Cants lagopus). P. 



5. Brown bear ( Ursus arctus). 



