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VV. H. BURT 



relationships, and the fossil record would indicate an early Tertiary 

 crossing. Late crossings are not indicated. This group has been on 

 the North American continent long enough to evolve into two genera 

 on the West Coast and three genera in eastern North America. 



Fig. 3. General distribution of shrews of the genus Sorex in North 

 America. Late crossings of the Bering land bridge are indicated. The 

 genus occurs also in Eurasia (Table I). 



A large area now separates the western and eastern kinds (Fig. 2). 

 In like manner the Eurasian moles have evolved into several genera, 

 all distinct from those of North America. Temperature probably 

 would not have been a factor in dispersal of moles, but soil type 

 would. Moles are able to survive in rather heavy soils as well as 



