DI8TRIBU 1 [l IN ()] M ELD M U E. 
will apply a- well t<» other genera and subfamilies of mice, while the 
term ** meadow mice" is not broad enough i«> 1 1 1 « - 1 1 1 « 1 < * all the sp< 
»f .1/ 
»i - i l : 1 1 •. i iii 
Field mice of the genus Mb rotus have -tout bodies, blunt, rounded 
muzzles, small eyes, and short ears often completely concealed in 
the fur. The tail is short and hairy; the soles of the feet arc naked 
or clothed with short hair-, and have five or sis foot pad- (plantar 
tubercles). The incisors are broad and not grooved. 
The molar teeth in all members of the genus, like the incisors <>f 
all rodents, gro\i continuously throughout the Life of the animal 
and do not develop roots. They arc prismatic in form, and the 
crown- -how triangular dentinal -pa..- surrounded by lines of 
harder enamel. These curious enamel patterns are of great impor- 
tance in the classification of the animal-, as they are but slightly 
affected by age and wear and an- remarkably constant for each 
species. 
About 165 living species and subspecies of Microtw have been 
gnized (1904), of which about 7^ are North American.'' Eight 
extinct fossil species have been described, and several of the living 
forms also have been found fossil. 
The genus Microtus is of wide distribution, covering practically 
the greater part of the northen hemisphere outside the tropical 
zoia — America north of the Tropic.-, all of continental Europe, and 
A-ia. except it- southern peninsulas. Great Britain ha- two species, 
but Ireland and the principal Mediterranean islands have none. 
The genus i- not found in South America, Africa. Australia, or the 
Australasian islands. While true mice (Mus) are found over a 
large part of the range of Microtus^ they do not extend so far north- 
ward and occur much farther southward. Microtus finds it- most 
Southerly extension in the Old World in Palestine and the southern 
-lope of tin 1 Himalaya Mountain-: in America, in southern Mexico 
and Guatemala. 
The range of a single species i- often remarkably great. Thus the 
typical form of the common meadow mouse of the United States 
(J/, pennsylvanicus) occur- over a lame part of at lea-t twenty-five 
State-, from Maine to the Dakota- and southward almost to 35 c 
north latitude. If the five subspecies (geographic races) are in- 
cluded, this range is almost doubled in extent. Another species, 
J/, mordax, occurs in most of the high mountain- from Colorado to 
California and from Arizona to Alaska. The meadow vole of Great 
o For key to the North American species and descriptions the reader may 
consult X. A. Fauna Xo. IT. Revision of American Voles of the Genus Microtus, 
by Vernon Bailey. T. 
10700— No. :'»1— 07 12 
