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.y 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. 
t Preble, E. A., “ Revision of the Jumping Mice.” 
