96 NEARCTIC SUB-REGIONS. [CH. II 



for the reunion of the regions is afforded by the con- 

 sideration that out of the 31 genera that they have in 

 common it is only possible -to withdraw three, as being 

 aquatic and therefore having a range of less significance, 

 and four which are exclusively or largely Arctic. Removing 

 in addition four genera of ubiquitous bats there are left 

 16 genera which are common to the two regions. This 

 calculation is made on the basis of genera admitted by 

 Mr Wallace ; on a more liberal estimate of what is meant 

 by a genus the number of genera would of course be 

 increased. 



The Nearctic region is usually divided into the four 

 following sub-regions: (I) Cali/omian, (II) Rocky Mountain, 

 (III) Alleghany, (IV) Canadian. 



I. Californian sub-region. This includes besides Cali- 

 fornia, a considerable part of British Columbia. It has 

 several peculiar genera of Mammals. Among them are 

 Enhydra a sea otter, Urotrichus a mole and Neosorex a 

 shrew. Haploodon, a rat-like rodent, is peculiar to this 

 sub-region, as are also the only North American repre- 

 sentatives of the bat famines Phyllostomidae and Nocti- 

 lionidse. The birds also embrace some peculiar forms. 

 The " road runner " Geococcyx and the aberrant Passerine 

 Chamaa, which Dr Shufeldt places near to the Tits, are 

 found here and nowhere else in the region. There are 

 other characteristic birds, but few that are absolutely 

 confined to the sub-region. 



II. Central or Rocky Mountain sub-region. The " big- 

 horn" sheep (Ovis montana), the Antilocapra and the goat 

 Haploceros are among the most characteristic Ungulates 



