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 which are morphologically close to the mallei of the subgenus Neotamias.
Figs. 1-3. Dorsomedial views of left malleus.
Fig. 1. Tamias striatus lysteri, No. 11920 sex?; from Carroll Co., New Hampshire.
Fig. 2. Eutamias sibiricus asiaticus, No. 199637 male NM; from I-mien-po, N. Kirin, Manchuria.
Fig. 3. Eutamias townsendii senex, No. 165 male; from Lake Tahoe, California.
Structure of the Baculum.—In discussing the baculum in Eutamias and Tamias, it seems desirable to do so in the light of the structure of the baculum in other sciurids.
The bacula of North American sciurids are divisible into six distinct types represented by those of the genera Spermophilus, Marmota, Sciurus, Tamiasciurus, Eutamias, and Glaucomys.
The type of baculum in Spermophilus is spoonshaped with a ventral process that is spinelike or keellike. Also, spines usually are present along the margin of the “spoon.” The base (proximal end) of the baculum is broad, and some species have a winglike process extending dorsally and partly covering a longitudinal groove. The shaft is more or less curved downward in the middle (see figs. [7, 10]).