Descriptions of East Asiatic Mammals 259 
VOLES, MEADOW MICE, AND LEMMINGS 
(SUBFAMILY MICROTIN^) 
The members of this large subfamily live for the most part 
in the cooler parts of the northern hemisphere. They are small, 
heavy-bodied Mice with short tails. If the teeth can be examined, 
it will be seen that the enamel pattern of the surface of the 
molars takes a more or less zig-zag course from front to rear 
(Fig. 57, c). The appearance of these teeth has been said to 
resemble a chain of prisms in end view. 
The Voles are customarily divided into two groups, a smaller 
and a larger. The first group, the Lemmini (Simpson), contains 
four genera of Lemmings, of which three are found in eastern 
Asia. The second group, the Microti, includes all remaining 
genera — a very large assemblage. These two groups are distin- 
guished by technical characters, including the positions of the 
roots of the lower incisor teeth within the bone of the lower 
jaw, in relation to the roots of the cheek teeth. The claws of 
True Lemmings become very large in winter, perhaps to aid 
them in scratching in the snow and ice for food. The Lemmings 
are confined to the northern parts of each hemisphere. Only 
the American genus Synaptomys extends southward for some 
hundreds of miles, chiefly along mountain ranges. 
The Collared Lemmings, genus Dicrostonyx, are a cir- 
cumpolar genus of thick-bodied, often short-tailed Voles. The 
ears are reduced to mere vestiges, and the openings can be 
closed by muscular contraction. The colors are mixtures of 
reddish and gray. The "collar" is often inconspicuous and may 
be absent. There is often a dark line along the middle of the 
back. The fur becomes white in winter. 
In this genus the typical species is the American D. hudsonius 
from Labrador. The best-known species from the Old World is 
D. torquatits, extending from Lapland through northern Asia 
