hyoid apparatus fused
in adults; conjoining tendon of anterior and posterior digastric muscles
rounded in cross section; keel on ventral surface of tip which curves
upward in baculum; tail less than 38 per cent of total length; five
longitudinal dark and four longitudinal light stripes present but two
dorsal light stripes at least twice as broad as other stripes; four
lateral dark stripes short.

_Geographic range._--Eastern Nearctic. West to Turtle Mountains, North
Dakota; eastern North Dakota, eastern South Dakota, Nebraska, Kansas,
and Oklahoma. South to southern Louisiana, Mississippi, Alabama,
northwestern Georgia. East to Atlantic Coast from South Carolina to Nova
Scotia. North to northeastern Quebec and southern tip of Hudson Bay.

DISCUSSION

Chipmunks are small striped squirrels that inhabit the Holarctic Realm
and that are found in similar niches in each of the three regions:
Palearctic, western Nearctic, and eastern Nearctic. Ellerman (1940) and
Bryant (1945) placed the chipmunks in three subgenera, corresponding to
the regions mentioned above, under the one genus _Tamias_. Critical
examination of new and old evidence reveals, nevertheless, that the
subgenera _Eutamias_ and _Neotamias_ of the genus _Eutamias_ are more
closely related to one another than either is to the genus _Tamias_.
This relationship can be seen clearly in the structure of the malleus,
baculum, hyoid apparatus, hyoid musculature, the presence or absence of
P3, the projection of the anterior root of P4 in relation to the
masseteric knob, and in the color pattern.

Because the genera _Eutamias_ and _Tamias_ occupy similar ecological
niches, the structural similarities that permit these animals to be
called chipmunks, show convergence, and thus can be assumed to be
adaptive. These similarities are in the molars, in shape of the skull,
in color pattern and in other features which have been used by many
systematists to interpret the phylogenetic relationships of the
squirrels. Pocock (1923:211), however, reviewed the taxonomic literature
on sciurids and wrote: "The conclusion very forcibly suggested by the
literature of the subject is the untrustworthiness of such characters."
Pocock (_op. cit._), correctly in my opinion, then established a
supraspecific classification of the sciurids based almost exclusively
on the structure of the baculum and glans penis. I have studied the
baculum in chipmunks and in all the major supraspecific groups