VOLES AND JUMPING-MICE 29 



Iceland and Greenland. There is no fossil evidence that voles 

 ever lived in any of these countries, where we might expect 

 them to have survived had any extensive migration taken place 

 from Great Britain to North America. Neither in Europe nor 

 in North America are there any fossil remains of the sub- 

 genus Microtus older than Pleistocene, if we accept Mr. 

 Barnum Brown's estimate of the age of the Potter Creek 

 deposits.* Nevertheless, it is possible that these voles origi- 

 nated in North America long prior to the Pleistocene Period. 

 If so I believe they made use of the Bering Strait land con- 

 nection rather than the North Atlantic one, in passing from 

 the New World to the Old. 



Evotomys, another genus found in the coastal district of 

 Labrador, has a range somewhat similar to that of Microtus. 

 It is closely allied to it and scarcely deserves the name of 

 "red-backed mouse " as the Americans call it, because it is 

 distinctly a vole, without any mouse-like characters about it. 

 The relationship between the American and Old World forms, 

 as in the case of Microtus, must be due to the existence of a 

 former land bridge across Bering Strait. 



The jumping-mice (Zapus), to which Zapus hudsonius 

 belongs, are, in many respects, an interesting group of 

 rodents. Somewhat kangaroo-like in their movements, they 

 are almost entirely confined to boreal North America. The 

 Labrador jumping-mouse is a variety of Zapus hudsonius, 

 which ranges from Alaska to Labrador and New York. A 

 single species of jumping-mouse (Zapus setchuanus) occurs in 

 China. f The theory that a former land bridge across Bering 

 Strait enabled its ancestors to traverse the northern Pacific 

 seems quite evident in this case. Yet we must not forget that 

 the American jumping-mice also have somewhat more dis- 

 tant relations in the Old World, the jerboas, from which the 

 remote ancestors of Zapus may possibly have descended. 



We need not at present deal with the other rodents or the 

 carnivores found in the coast district of Labrador, as most of 

 these will be referred to again in subsequent chapters. The 

 animals that have just been alluded to show us that the 



* Brown, Barnum, " Conard fissure," p. 208. 



f Preble, E, A., " Revision of the Jumping Mice." 



