PHENACOMYS 



of the genus Lemmus, although this is of comparatively rare 

 occurrence since Dicrostonyx is usually not as abundant as 

 Lemmus. At such times Dicrostonyx swim streams and press 

 on in the face of all obstacles. 



The young are bom in early summer and usually number 

 three to a litter. 



Genus Phenacomys ^ 



Dentition: Incisors, \; Canines, {] ; Premolars, J] ; Molars, | = i6. 



Phenacomys. — Phenacomys intermedius 



and related forms 



Names. — Phenacomys; Lemming Mouse. For want of a 

 good colloquial or vernacular name for the members of the 

 genus, Howell suggests the generic term as the common group 

 name. The two arboreal species are called Tree Mice, 



General Description. — A small Mouse very similar in 

 external appearance to some of the Meadow Mice from which 

 it may be certainly distinguished only by cranial and dental 

 characters (rooted molars as compared to unrooted molars in 

 Microtiis). Form normal and mouse-like; legs short; tail 

 short (long in some forms of the genus), pelage rather long and 

 loose; ears rather small and almost hidden in fur of head; 

 mammee eight in number; plantar tubercles six (as far as 

 known) ; a rare Mouse in most localities. Plate XXX. 



Color. — Sexes colored alike; some seasonal variation, but 

 little is known on this point. 



Upperparts. — Color variable, from tawny olive to umber, 

 pelage slate-colored at base and showing through to some 

 extent. In winter grayer. Tail bicolor. 



Underparts. — Whitish, sometimes with buffy wash. 



Immature pelage darker than adult. 



Measurements. — Sexes of approximately equal size. Total 

 length, 5.7 inches; tail vertebrae, 1.2 inches; hind foot, .7 

 inch. 



Geographical Distribution. — Found in the colder zones and 

 mountain summits of Canada and the western United States. 



Food. — Vegetation, seeds, stems, soft parts of plants; in 

 case of two species, needles of conifers. 



^ For a recent and comprehensive revision of this genus see A.B. Howell, 

 North American Fauna, No. 48, 1926. 



