erior end, to the bulla at a point slightly
ventral and posterior to the auditory meatus.

In the genus _Eutamias_ the hypohyal and ceratohyal are completely fused
in adults, the suture between these two bones being visible in juvenal
specimens (see fig. 12).

In the genus _Tamias_ the hypohyal and ceratohyal remain distinct
throughout life. The hypohyal may frequently be divided into two parts,
a variation which is also present in _Marmota_.

The musculature associated with the hyoid apparatus in _Eutamias_ and
_Tamias_ is as described by Bryant (1945:310, 316) for the Nearctic
squirrels. However, the conjoining tendon of the anterior and posterior
pairs of digastric muscles is ribbonlike in _Eutamias_ and rodlike
(rounded in cross section) in _Tamias_.

_The presence or absence of P3 and the projection of the anterior root
of P4 in relation to the masseteric knob._--Only rarely is P3 absent
in _Eutamias_ or present in _Tamias_. P3 in specimens of old adult
_Eutamias_, shows wear, thus suggesting that P3 is functional in older
chipmunks. In _Eutamias_, which normally has a P3, the anterior root of
P4 projects to the outside of the masseteric knob, whereas in _Tamias_,
which normally lacks a P3, the anterior root of P4 projects directly
to the masseteric knob or to the lingual side of this structure. The
projection of the anterior root of P4 seems to be correlated with the
presence or absence of P3. However, in a specimen of _Tamias striatus
rufescens_ (No. 11117 KU), the left P3 is present, yet the anterior
root of P4 still projects to the lingual side of the masseteric knob.

Ellerman (1940:48) and Bryant (1945:368-369, 372) think that the
presence or absence of P3 is not of generic significance in chipmunks,
since P3 is vestigial and probably is in the process of being lost, and
since this character is rarely used as a generic character in other
sciurids. I think that the presence or absence of P3, together with the
projection of the anterior root of P4 in relation to the masseteric
knob, is of generic significance, for, squirrels in general have
retained the dentition and dental formula of a primitive rodent, and
any change in the pattern of the teeth or in dental formula is, in my
opinion, of a fundamental nature.

_Length of tail in relation to total length._--The tail in _Eutamias_ is
more than 40 per cent of the total length, whereas in _Tamias_ the tail
is less than 38 per cent of the total length. In thi