THE MEADOW MICE. 



505 



ferred from one locality to another often find a niche not occupied 

 by the native fauna, and with the absence of natural enemies they 

 may multiply very rapidly and become a serious pest. 



Genus Microtus Schrank. 



Microtus Schrank, Fauna Boica, Vol. I, 1st Abth., p. 72, 1798. 

 Miller, N. Am. Fauna. No. 12, p. 9. 



Dental For7nula.~l, ^E]; C, Pm, '^l] M, = 16. 



Generic characters. — Form thickset, with short, heavy legs, the 

 hind pair of which are generally flexed at the ankle joint so that 

 the body is carried close to the ground; head broad and blunt; 

 eyes small, ears concealed b}^ fur ; tail always shorter than the body 

 without the head, often much shorter. 



The skull is broad, flattened dorsally, and strongly built. The 

 upper incisors are never grooved; lower incisors long, the roots ex- 

 tending along the lower jaw almost to the angle, passing outside the 

 last molar and inside the other two ; molars with the enamel folded 

 into loops which extend across the tooth, or triangles which have 

 their bases along the middle line ; molars with the bases the same 

 shape of the crowns and not divided into prongs or roots. 



The range of the genus includes most of the north temperate 

 zone in both hemispheres. The mice of this genus are known as 

 voles or meadow-mice. About 75 forms are known from North 

 America and of these, four are found in Indiana. The Indiana 

 species belong to three subgenera. They may be distinguished by 

 the following key : 



A. Tail short (less than l inch); color brownish with dense soft, velvety fur; 

 mammae four; skull flat. (Subgenus Pitymys). 

 B. Ear conspicuous above the fur; color dark rich brown; tail nearly one 

 inch. auricularis. 

 BB. Ear small; color dull brown; tail paler underneath than above. 



scalopsoides. 



AA. Tail about an inch and a quarter or longer; fur coarse and grizzled; mam- 

 mae more than four. 

 B. Color dark brown, grizzled with black; tail about an inch and three- 

 quarters; mammae eight. (Subgenus Microtus.) pennsylvanicus. 

 BB. Color black and white or yellowish in a sort of pepper-and-salt mix- 

 ture; tail less than one and a half inches; mammae six. (Subgenus 

 Pedoniys). ochrogaster 



