National Science
Foundation, and the United States Navy, Office of Naval
Research, through contract No. NR161 791.

EVALUATION OF CHARACTERS

The following paragraphs treat the characters listed by Howell,
Ellerman, and Bryant, and such additional characters as I have found
useful in characterizing the genera and subgenera of chipmunks. Some of
the findings, I think, illustrate how study of such mammalian structures
as the baculum, malleus, and hyoid apparatus--structures that seem to
be little influenced by the changing external environment--clarifies
relationships, if these previously were estimated only from other parts
of the anatomy of Recent specimens.

The structural features and characters to be discussed, or listed, below
may be arranged in three categories as follows: 1) Characters in which
the subgenera _Eutamias_ and _Neotamias_ agree but are different from
the genus _Tamias_; 2) Characters in which the subgenus _Eutamias_
and the genus _Tamias_ agree but are different from the subgenus
_Neotamias_; 3) Structural features that are too weakly expressed to
be of taxonomic use.

CHARACTERS IN WHICH THE SUBGENERA EUTAMIAS AND NEOTAMIAS AGREE, BUT
DIFFER FROM THE GENUS TAMIAS

_Structure of the Malleus._--The malleus in chipmunks is composed of
a head and neck, a manubrium which has a spatulate process at the end
opposite the head, and a muscular process situated about halfway between
the spatulate process and the head of the malleus. An articular facet
begins on the manubrium near the neck and spirals halfway around the
head of the malleus. A lamina extends from the anterior edge of the head
and neck, tapers to a point and joins the tympanic bulla anteriorly
where there is a suture between the lamina and bulla. The lamina is one
half as long as the rest of the malleus (see figs. 1-3).

The head of the malleus in _Tamias_ is clearly more elongated than in
_Eutamias_. The plane formed by the lamina in _Eutamias_ makes an angle
of approximately 90 degrees with the plane formed by the manubrium; in
_Tamias_ the two planes make an angle of approximately 60 degrees.

Examination of series of mallei of _Eutamias_ and _Tamias_ indicate that
there is slight individual variation, slight variation with age, and no
secondary sexual variation. Intraspecific variation in the subgenus
_Neotamias_ is slight, consisting of differences in size. Specimens
of the subgenus _Eutamias_ from Manchuria have mallei