June 7, 1924 
Variation in Microtus Montanus Yosemite 
981 
upon these members are lighter and somewhat gray. This is longer upon the 
feet of fully adult examples than upon younger ones, thus causing the feet of 
mature animals to appear paler. 
An arrangement of all males and females in two lots according to sex and with 
reference to the head and body measurement corroborates, on the whole, the 
above observations on coloration. The results, however, are not by any means 
all that could be desired, for probably 25 per cent of the specimens do not occupy 
the exact positions in the series where one considers, after a very careful study of 
the pelages, that they should belong. A regrouping of the skins with reference 
to the condylo-basilar length of the skulls gives results that are much more con¬ 
vincing, and there are then very few of the specimens which seem to belong in 
other positions. A third regrouping according to weight is a trifle more satis¬ 
factory still for males. Weights of females, however, can not be thoroughly 
uniform with development, because of the frequent presence of embryos. As 
the difference between these last two arrangements is practically nil, it is perhaps 
wiser to select the condylo-basilar criterion as the most desirable basis for group¬ 
ing the skins according to age as indicated by pelage. 
Table I .—Measurement of males taken in the flesh, weights, and braincase capacity 
arranged in descending sequence according to the condylo-basilar measurement of 
the skulls 
1 
Measurements 
I 
Brain- 
Collection number 
[Head and 
j body 
Tail 
Hind 
foot 
Weight 
case 
capacity** 
3835 .- __ 
Mm. 
128 
Mm. 
53 
Mm. 
23 
Grams 
67.0 
130 
3837______- 
133 
55 
22 
68.6 
120 
3812...... 
133 
47 
23 
70.7 
109 
3826 ....... 
129 
48 
21 
60.5 
128 
3853 .... 
126 
47 
23 
59.8 
114 
3825....... 
132 
43 
22 
59.7 
113 
3854____ 
127 
47 
22 
55.6 
106 
3822 _... __ 
132 
53 
22 
66.0 
119 
3818_____ 
134 
( b ) 
21 
61.4 
113 
3864 _ _ 
120 
48 
21 
58.8 
126 
3846 .. ___ 
118 
49 
21 
51.0 
110 
3855 _ 
125 
47 
23 
53.2 
120 
3848 ...... 
115 
55 
22.5 
45.3 
119 
3862 _ . ___ ___ 
120 
45 
21 
48.7 
110 
3883 . „ ___ 
120 
53 
22 
49.8 
118 
3820 _ ____ 
122 
48 
21 
47.0 
105 
3841 ___ 
113 
48 
22 
42.2 
104 
3870 . ^ . ___ 
116 
42 
22 
46.2 
107 
3847 ______ 
111 
49 
23 
43.7 
116 
3867 ____ 
115 
52 
22 
45.5 
112 
3887 ...... 
110 
46 
22 
35.6 
110 
3814 ____ 
111 
49 
23 
38.5 
115 
3849 . . ___ 
111 
47 
23 
43.8 
106 
3801 . ___ 
117 
38 
21.5 
38.8 
99 
3857 ______ 
97 
41 
22 
26.5 
96 
Averages c - . .... 
122 
48.2 
22 
52.7 
113. 3 
a In number of pellets of No. 10 shot. 
b Tail damaged: Measurement not considered. 
c Averages of 19 males, the largest two and smallest four specimens being excluded. 
