various sorts, also grass. From four to six young are born in a litter, and 

 the breeding season extends from May into July. 



Xo. 12. Nest of Colorado Red-backed Mouse, Evotomys Capper! j^nloi; 



on ground under piece of building paper. Photograph by 

 Albert Haanstad. 



MOUNTAIN LEMMING MICE OR VOLES. 



It is difficult so to describe the Mountain Voles that a layman can 

 distinguish them from the true Meadow Mice. They are small animals 

 with proportionately shorter tails than most of our species of Meadow 

 Mice. The most certain distinguishing characteristic is the molar teeth, 

 each of which has two roots in the adult animals, while the molar teeth 

 of the Meadow Mice have no roots, the portion which is seated in the jaw 

 being the same shape as the external portion. 



The name Pheiiaconiys means "false mouse", and was given because 

 the members of the genus had* been placed in Microtus because of their 

 external resemblance to that genus. The genus is North American and is 

 confined to the boreal regions of the continent and higher elevations of 

 the Rocky and other western mountains. There are two species in Colo- 

 rado, the Mountain Lemming Mouse or Idaho Mountain Vole, Phenacomys 

 oropliilu^, and Treble's Lemming Mouse or Mountain Vole, P. preblei. 



Vernon Bailey, in his account of the mammals of the Glacier National 

 Park, says this species lives in burrows in the grassy parks, and makes 

 tiny runways through the grass from one burrow to another, but both 

 the burrows and runways are well concealed. The animals are largely 

 nocturnal. They seer- to eat much green vegetation. The nests appear 

 to be entirely underground. They apparently have in a season several 

 litters of from four to six young. 



At present Preble's Mountain Vole is known only from the type local- 



20 



