P4 in relation to masseteric knob.

buccal. lingual. Length of tail in relation to total length. more than 40 per cent. less than 38 per cent. Width of longitudinal stripes. subequal. median pair of light stripes twice as wide as others. Length of lateral longitudinal light stripes. outermost pair short. both pairs short.

 

It must be pointed out here that the subgenus Neotamias always differs from both the subgenus Eutamias and the genus Tamias in pointed versus rounded pinna of ear (see table 2) and in the supraorbital notch being slightly posterior to or even with, instead of distinctly anterior to, the posterior notch of the zygomatic plate. The relative position of these two notches, however, seems to be a matter of relative (heterogonic) growth. Further, the base of the postorbital process of the frontal usually is narrower (relative to the length of the process) in the subgenus Neotamias but there is a gradation in this feature in Neotamias culminating in the species E. townsendii in which the bases of the processes are relatively as broad as in the subgenus Eutamias and the genus Tamias. The same condition obtains in the shape of the infraorbital foramen which is subovate to rounded in the subgenus Neotamias and always rounded in the other chipmunks.

 

Table 2.—Characters by Means of Which the Subgenus Eutamias and the Genus Tamias May Be Distinguished from the Subgenus Neotamias

 

These differences of Neotamias are so slight in comparison with the similarities (ten features mentioned above) that Neotamias here is accorded only subgeneric rank under the genus Eutamias, instead of generic rank.

Howell’s (1929) arrangement of the genera and subgenera of chipmunks is judged to be correct as indicated by the following arrangement that I propose.

Genera and Subgenera

Genus Eutamias Trouessart

Eutamias Trouessart, E. L. Catal. Mamm. viv. et foss., Rodentia, in Bull. Soc. d’Etudes Sci. d’Angers, 10:86-87, 1880. Type Sciurus striatus asiaticus Gmelin.

Eutamias, Merriam, C. H., Proc. Biol. Soc. Washington, 11:189-190, July 1, 1897.

Eutamias, Howell, A. H., N. Amer. Fauna, 52:26, November 30, 1929.

Tamias, Ellerman, J. R., The families and genera of living rodents. British Mus. (Nat. Hist.), 1:426, June 8, 1940.

Tamias, Bryant, M. D., Amer. Midland Nat., 33:732, March 1945.

Diagnosis.—Skull lightly built, narrow; postorbital process light and weak; lacrimal not elongated; infraorbital foramen lacks canal, relatively larger than in most sciurids; P3 present; head of malleus not elongated; plane of manubrium of malleus 90 degrees to plane of lamina; hypohyal and ceratohyal bones of hyoid apparatus fused in adults; conjoining tendon between anterior and posterior sets of digastric muscles ribbonlike; keel on dorsal side of tip of baculum; tail more than 40 per cent of total length; five longitudinal dark stripes evenly spaced and subequal in width; two lateral dark stripes short.

Subgenus Eutamias Trouessart

Eutamias Trouessart, E. L. Catal. Mamm. viv. et foss., Rodentia, in Bull. Soc. d’Etudes Sci. d’Angers 10:86-87, 1880. Type Sciurus striatus asiaticus Gmelin.

Eutamias, Howell, A. H., N. Amer. Fauna, 52:26, November 30, 1929.

Eutamias, Ellerman, J. R., The families and genera of living rodents. British Mus. (Nat. Hist.), 1:426, June 8, 1940.

Eutamias, Bryant, M. D., Amer. Midland Nat. 33:732, March 1945.

Diagnosis.—Size large; lambdoidal crest moderately developed; supraorbital notches distinctly anterior to posterior notch of zygomatic plate; baculum with faint keel on dorsal surface of tip which curves upward; pelage coarse; ears broad, rounded, of medium height.

Geographic range.—Palearctic. West to Dvina and Kama rivers, Vologda, and Kazan, in European Russia. South to southern Ural Mountains, Altai Mountains; Kansu, Szechwan, Shensi, Shansi, and Chihli provinces of China; Manchuria and Korea. East to Hokkaido Island, Japan; Kunashiri Island, southern Kurile Islands; Sakhalin Island, and Yakutsk, Siberia. North nearly to Arctic Coast in Siberia and European Russia (Ellerman and Morrison-Scott 1951:503).

Subgenus Neotamias Howell

Neotamias Howell, A. H., N. Amer. Fauna, 52:26, November 30, 1929. Type, Eutamias merriami J. A. Allen [=Tamias asiaticus merriami J. A. Allen].

Neotamias, Ellerman, J. R., The families and genera of living rodents. British Mus. (Nat. Hist.), 1:426, June 8, 1940.

Neotamias, Bryant, M. D., Amer. Midland Nat., 33:372, March, 1945.

Diagnosis.—Size small to medium; lambdoidal crest barely discernible; supraorbital notches even with, or posterior to, posterior notch of zygomatic plate; baculum with distinct keel on dorsal surface of tip which curves upward; pelage silky; ears long and pointed.

Geographic range.—Western Nearctic. West to Pacific Coast. South to Lat. 20°30' in Baja California and to northwestern Durango and southeastern Coahuila, Mexico. East to eastern New Mexico, westernmost Oklahoma, eastern Colorado, Wyoming, northwestern Nebraska, western and northwestern South Dakota, western and northwestern North Dakota, northeastern Minnesota, northern Wisconsin and Upper Peninsula of Michigan, and eastern Ontario. North to