208 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XI. 



Subfamily MICROTIN^. 



A subfamily confined to the northern portions of the old and new 

 worlds. The crowns of molars show irregular enamel loops or triangles. 



Genus EVOTOMYS Coues. 



Evotomys Coues, Proc. Acad. Nat. Sci. Phila., 1874, p. 186. Type 



Mus rutilus Pallas. 



Skull narrow and slender; front teeth (incisors) without grooves; 

 molars with pronged roots; crowns of molars with irregular triangles; 

 tail comparatively short; middle of back (normally) reddish brown, in 

 decided contrast to the color of the sides of body; mammae 8. 



Dental formula: I. - > C. - Pm. - M. ^ ^= 16. 

 i-i o-o o-o 3-3 



Evotomys gapperi (VIGORS). 

 RED-BACKED MOUSE. RED-BACKED VOLE. 



Arvicola gapperi VIGORS, Zool. Jour., V, 1830, p. 204. KENNICOTT, Agr. Rept. 



for 1857, U. S. Patent Office Rept., 1858, p. 88 (Wisconsin, Minnesota). STRONG, 



Geol. Wis., Surv. 1873-79, I, 1883, p. 439 (Wisconsin). 

 Hypudaus rutilus var. gapperi HERRICK, Geol. & Nat. Hist. Surv. Minn., Bull. 



No. 7, 1892, p. 194 (Minnesota). 

 Evotomys gapperi BAILEY, Proc. Biol. Soc. Wash., XI, 1897, p. 122 (Minnesota, 



Ontario, etc.). SNYDER, Bull. Wis. Nat. Hist. Soc., II, 1902, p. 116 (Dodge Co., 



Wisconsin). JACKSON, Bull. Wis. Nat. Hist. Soc., VI, 1908, p. 22 (Wisconsin). 



Type locality Vicinity of Lake Simcoe, Ontario. 



Distribution The Atlantic states from Pennsylvania northward and 

 west along the northern border of the United States to Minnesota 

 and in Canada to the Rocky Mountains. 



Special characters A broad rufous chestnut stripe on middle of back 

 extending from the crown to the rump; sides of body grayish buff, 

 sometimes with a slight olive tinge but always strikingly different 

 from the color of the back; tail comparatively short. 



Description Normal phase: A broad stripe of rufous chestnut from 

 the back of the head extends down middle of the back to the rump ; 

 sides of body and fore part of head and face grayish buff, sometimes 

 faintly tinged with olive; a dusky mark at base of the whiskers; 

 under parts ashy or whitish, often faintly tinged with buff; the bases 



