212 Mammals of Eastern Asia 
to one another than to other rodents, may at first thought seem 
strange. Yet everyone realizes that Ground Squirrels are with- 
out question merely short-tailed Squirrels with burrowing hab- 
its. A moment's thought will show that a Woodchuck is just a 
thick-bodied, oversized kind of Ground Squirrel. Beavers also 
are essentially large Squirrels, although they manifest many 
peculiar adaptations that fit them for life in water, including the 
broadened paddle-like form of the tail. Study of fossil Beavers 
has shown that much experimental evolution took place in the 
Beaver world before the present-day Beaver came upon the 
scene. 
The Flying Squirrels, sometimes considered a subfamily of 
the Sciuridse, are here treated as a family, the Pteromidse. 
SQUIRRELS AND MARMOTS (FAMILY SCIURID^) 
It is difficult to offer a succinct list of the squirrel-like forms 
belonging to this family. But in very broad terms the following 
is a synopsis of the Squirrels of eastern Asia: Tufted-eared 
Squirrels of the north (true Sciurus) ; Striped Squirrels of the 
warmer parts (Lariscus, Menetes, and Tamiops) ; usually un- 
striped, typically squirrel-like genera (Ratufa, Callosciurus) ; 
Long-nosed Squirrels (Dremoniys, Rhinosciurus) ; Chipmunks 
and Rock Squirrels (Eutamias, Sciurotamias, Rupestes) ; the 
extremely short-tailed Susliks (Citellus) and Woodchucks 
(Marmota). The largest of the genera listed is Callosciurus, a 
genus of often brilliantly colored, medium-sized Tree Squirrels 
found mainly in the oriental tropics. 
The Eurasian or True Squirrels, genus Sciurus, contain, 
according to modern views, only the typical species S. vulgaris, 
and S. anomalus of southwestern Asia, which is sometimes 
treated as a distinct subgenus, Tenes. The entire system of the 
American Tree Squirrels is also thought to be related to Sciurus. 
The name "Sciurus" has at various times been employed for the 
major part of the Squirrels of the world, which is readily 
