MOUNTAIN FAUNAS 87 
and as these are typical denizens of cold steppes, it is 
natural that they should occur also in the steppe region 
of lofty mountain chains. In Europe the Alpine marmot 
is found in the Alps, the Pyrenees, and the Caucasus, 
though it once occurred on the low ground also. In 
Central Asia many kinds of marmots occur, though 
none extend to the south of the Himalayas. The 
Himalayan marmot, allied to the bobac of the steppes, 
is limited to the region above the tree limit, that is, to 
the barren wastes which most nearly resemble the home 
of the bobac, the usual elevation being 12,000 to 13,000 
feet. In North America we have similarly a Rocky 
Mountain marmot, resembling in habits the Alpine form. 
The voles (Arvicola) are well represented in mountain 
regions, the genus showing a remarkable tendency to 
run into varieties, or species, in particular localities. 
Thus in the Alps and Pyrenees there occurs the very 
curious Alpine or snow vole (A. nivalis), which is some- 
times pure white, but is structurally very near the 
continental field vole and the bank vole. It differs 
notably from these forms in its habits, for it lives high 
up the mountains, even above the snow-line. It has 
been found on the Finsteraarhorn at a height of 12,000 
feet, but on account of its habits is rarely seen. It 
appears to live actually beneath the snow, making 
runs beneath it after the fashion of the Arctic lemming, 
in its search for vegetation. Other mountain species 
occur in the Himalayas and Tibet. 
South America, with its paucity of ungulates, has 
a considerable number of peculiar mountain rodents. 
Thus the common chinchilla (Chinchilla lanigera), with 
its soft thick fur, inhabits the higher parts of the Andes, 
living in rocky ground, and displaying marvellous 
agility. A larger form (Lagidium cuvieri) inhabits the 
