RODENTIA-SCIURINAE-TAMIAS. 
291 
TAMIAS, Illiger. 
Taviias Illigier, Prod. S)-st. Mam. ct Av. 1811, 83. 
Aud. & Bach. N. Am. Quad. I, 1849, 64. 
Tenotis, Rafinesqce, Am. Month. Mag. I, 1817, 362. 
Check pouches ample, extending to the occiput. Tail shorter than the bocfy, not bushy. The species with three to five 
dark dorsal stripes. Permanent upper molars four. The anterior basal plate of the zygoma perforated by a nearly circular 
foramen. 
The genus Tamias hears somewhat the same relation to the squirrels that Spermophilus or 
rather Otospermophilus does to Ardomys. It is composed of a very limited number of species, 
two of which occur in Europe and Asia and the remaining four or five in North America. All 
are marked with a median dark dorsal stripe, usually with two others on each side ; the 
intervals between the stripes either of the ground color or lighter. 
The cheek pouches are ample in Tamias, and are capable of great distension, so as to hold a 
large supply of food. They open anterior to or alongside the molars, and reach hack almost to 
the shoulder. 
The tail is short, less than the body, and the hairs, though longest on the sides, are com¬ 
paratively short; nor is the tail at all bushy. The feet are large, and the claws well developed, 
in accordance with the fossorial habits of the species. 
The skull is depressed and narrow and tapers anteriorly to the end of the considerably 
elongated muzzle. The dorsal outline is quite convex. The post orbital processes are slender 
and styliform. The zygomatic arch is very gently and uniformly curved in its inferior outline 
from the temporal bone to where it melts into the intermaxillary on the upper part of the 
snout, instead of having a distinct angular bend upwards just opposite the inferior edge of the 
zygomatic process of the maxillary. In this character it differs from all other Sciurinae. The 
plane of the zygomatic plate of the maxillary, too, is more oblique to the vertical plane of the 
axis, and there is a very distinct, nearly circular, foramen perforating the base of this plate, a 
character entirely peculiar to Tamias among the squirrels. The tubercle below the foramen is 
quite distinct. The permanent molars are only four in number and are quite small. They 
are quite peculiar in having the plane of the grinding surfaces horizontal anteriorly, then 
twisting gradually outwards, rendering the crown of the last molar quite oblique. The level 
of the crown of the last molar, too, is considerably higher than that of the first, the external 
outline of the alveoli rising behind in a similar manner, so that if produced it would intersect 
the parietal bone considerably in advance of the occiput. Both outlines of the molar series are 
gently convex, the anterior molars themselves a little wider apart than the posterior. 
The lower molars correspond with the upper ones in the twisting of the plane of the grinding 
surface and its gradual elevation posteriorly. The lower jaw is much slenderer than in the 
true squirrels; the coronoid process is narrow, elevated, and much curved. The upper 
incisors are compressed laterally ; as in Sciurus the lower have the antero-posterior dimensions 
much less in proportion. 
The skull of Tamias exhibits a considerable resemblance in shape to that of the Tamias-like 
Sphermophiles. It is, however, much more depressed. The anteorbital foramen is in the 
