Microtinae- Voles 
93 
a. Tail about as long as the body, naked and scaly; ears naked. 
Mus, p. 137 
Subfamily MICROTINiE 
The members of this family are externally distinguished as a 
rule by their clumsy heavy build, their small eyes, blunt 
muzzles, small ears, and shorter limbs and tails; skull short 
and broad, nasals short, hardly extending beyond the pre- 
maxillae; swelling of the root of the lower incisors chiefly on the 
inside of the mandible; molars rootless or imperfectly rooted, 
composed of longitudinal rows of triangular prisms placed 
alternately. 
This subfamily containing the Voles is confined to the 
Palearctic and Nearctic regions {i.e., the northern portions 
of the Old and New Worlds). 
Genus MIC ROT US (Grk. mikros, small, + otus, ear, small- 
eared). 
Microtus Schrank, Fauna Boica., {., pt. i, p. 72 (1798). Type 
M. arvalis. 
Revision, Bailey N. A. Fauna, No. 17 (igoo). 
Small voles with rounded tails as long as and usually longer than 
the hind feet ; first digit of the fore feet with a small rudimentary 
pointed claw with a flat nail. Dentition, i. m. | X 2 = 16; 
lower incisors with the roots extending far behind and on the outer 
side of the molars; upper incisors not grooved; molars rootless, the 
outer and inner reentrant angles approximately equal. 
The members of this large genus are to be found all over 
the temperate portions of Europe, Asia, and North America, 
ranging north to the extreme limit of mammalian life and 
south to the edge of the tropics. According to Elliot's Check- 
list some 53 species are found in North America, distributed 
among nine subgenera. Hitherto only five species have 
been found within the limits of Colorado, representing 
three subgenera; these can be distinguished as follows: 
