el, 10,000 ft., on
trail, 2 WC; Buffalo Pass, 10,380 ft., 1 WC; Buffalo Pass
road, 10,130 ft., 1 WC. _Larimer Co._: 2 mi. E Log Cabin,
7,450 ft., 1 WC; Estes Park, 7,600 ft., 1; 1-1/2 mi. SW Estes
Park, 1; 2-1/2 mi. SW Estes Park, 2; 3-1/2 mi. SW Estes Park,
1; 12 mi. SW Estes Park, 1. _Rio Blanco Co._: 1 mi. NW Pagoda
Peak, 10,400 ft., 1. _Boulder Co._: Long's Peak, 7 BS; 1 mi.
NE Ward, 10,000 ft., 1; 3 mi. S Ward, 9,000 ft., 5; 1/2 mi. E
and 3 mi. S Ward, 9,400 ft., 1; 1 mi. S Gold Hill, 8,200 ft.,
1. _Clear Creek Co._: Davidson Mine, 3 mi. SW Idaho Springs,
1; Georgetown, 1 CM. _Jefferson Co._: Silver Plume, 1 CM.
_Park Co._: Tarryall Creek Camp, 8,700 ft., 1 WC. _Gunnison
Co._: S side Crested Butte Mountain, 9,500 ft., 1 WC; mouth
of Virginia Basin, Gothic, 1 FC.

DISCUSSION

The chipmunks that heretofore have been assigned to the species
_Eutamias quadrivittatus_ are here assigned to two species, _E.
quadrivittatus_ and _E. umbrinus,_ for the following reasons:

1. The baculum of _E. quadrivittatus_ differs from that of _E.
umbrinus_ in having a narrow base (see figs. 3, 4). This difference
permits any specimen which has an associated baculum to be readily
identified to species.

2. The cranial breadth in the subspecies of _E. quadrivittatus_ is
significantly larger than in the subspecies of _E. umbrinus_.

3. Specimens of _E. umbrinus_ are darker than any specimen of _E.
quadrivittatus_.

4. Where the geographic ranges of _E. quadrivittatus_ and _E.
umbrinus_ come close to one another (probably they meet at some
places), _E. umbrinus_ occupies a higher position in terms of
life-zones. Wherever either of these two species, but not the other,
occurs on a mountain the species occupies both the higher and lower
life-zones.

[Illustration: FIGS. 3 and 4. Baculum of _Eutamias
quadrivittatus quadrivittatus_, No. 35648/47919 BS; from
Canon City, Fremont Co., Colorado. Figure 3, lateral view of
right side; figure 4, dorsal view.

FIG. 5. Baculum of _Eutamias umbrinus umbrinus_, No. 38062;
from Paradise Park, 21 mi. W and 15 mi. N Vernal, 10,050 ft.,
Uintah Co., Utah. Lateral view of right side.

FIG. 6. Baculum of _Eutamias umbrinus montanus_, No. 20105;
from 1/2 mi. E and 3 mi. S Ward, 9,400 ft., Boulder Co.,
Colorado. Dorsal view.]

The differences between _E. quadrivittatus_ and _E.