266 Mammals of Eastern Asia 
placed in Arvicola are currently considered to be Microtus 
(Meadow Mice). 
The Pine Mice, genus Pitymys, are an offshoot of the 
Meadow Mice that have become burrowers. They can be dis- 
tinguished from these by the fact that their females have 4 
nipples instead of 8. This genus conspicuously exemplifies dis- 
continuous distribution. It occurs from central and southern 
Europe to Asia Minor, and reappears in the eastern and south- 
ern United States and in Mexico. Although no living species 
are known from eastern Asia, a fossil, P. simplicidens, is 
recorded from southwest of Peking, China. 
The Meadow Mice, genus Microtus, are typically somewhat 
shaggy-haired, short-tailed Mice, colored brownish gray above, 
light gray beneath. The species are very numerous. They have 
been grouped together by various students into a number of 
subgenera, some of which can be distinguished only with con- 
siderable difficulty. Many of the species are of economic im- 
portance, for they become very numerous periodically and then 
injure crops. They are generally controlled by such predators 
as foxes and owls. As they may have a new generation every 
50 days or so, and from 4 to 9 may be born in a litter, it is easy 
to appreciate how rapidly a population of field Mice may in- 
crease under favorable conditions. The subgenera of Microtus 
occurring in the oriental parts of Asia are four: Phaiomys, 
Neodon, the narrow-skulled Stenocranius, and Microtus 
proper. 
The subgenus Phaiomys (including Lasiopodomys) is 
primarily Himalayan and central Asiatic. The typical species is 
P. leucurus (= blythi) from Tibet; that of Lasiopodomys is L. 
brandtii from Mongolia. All species have undergone slight re- 
duction of the ears and tail and enlargement of the claws. The 
thumb has a claw instead of a nail. Two additional species are 
known, mandarinus from Shansi and Shensi and everesti from 
Mt. Everest, 17,000 feet. All are somewhat fossorial. 
