Comparisons.—From M. p. alcorni (see [description]), M. p. tananaensis differs as follows: Smaller in all measurements taken except alveolar length of upper molariform tooth-row which is the same; color of upper parts darker, more richly brown and less gray; underparts darker; zygomatic arches less massive and narrower; auditory bullae larger and more inflated.
From M. p. drummondii (see [comparisons] under M. p. alcorni), M. p. tananaensis differs as follows: Larger in all cranial measurements taken except nasal length which is the same; color everywhere slightly darker; wider across zygomatic arches; zygoma thicker; nasals, relative to length of skull, shorter; auditory bullae larger and more inflated.
Remarks.—For the most part the material available of this subspecies consisted of subadults; however, comparison of adults with those of adjacent subspecies indicates that this subspecies can be distinguished by color of the upper parts, cranial measurements, and size of the zygomatic arches and the auditory bullae. Specimens from 14 miles east and 25 miles north of Fairbanks are especially dark. One subadult (No. 21467, UKMNH) has blackish hair on the feet and a blackish unicolored tail. No. 241696, USBS, an old adult female, from Ketchumstock, is larger.
The specimens referred to this subspecies, vary some in color, but vary less in cranial characters. Additional adults are needed from western Alaska to determine how far this subspecies extends down the valley of the Yukon River. Bailey (1900:24) lists one specimen from Nulato, as drummondii; I have not seen it but on geographic grounds tentatively assign it to M. p. tananaensis.
Measurements.—Measurements of the type specimen are as follows: Total length, 160; length of tail, 40; condylobasal length, 26.0; basal length, 24.9; length of nasals, 6.7; zygomatic breadth, 14.5; breadth across auditory bullae, 12.5; alveolar length of upper molariform tooth-row, 6.2. Two specimens from Eagle (Nos. 128295 and 128320, USBS) have the following measurements respectively: 161, 154; 37.5, 36; 25.3, 25.4; 23.8, 23.9; 6.5, 6.8; 14.5, 14.6; 11.9, 12.3; 6.1, 6.1.
Specimens examined.—Total 34, distributed by localities of capture as follows and unless otherwise stated in the University of Kansas Museum of Natural History: Alaska: Near Buster Creek, Chatanika River, 1 (USBS); Chatanika River, 700 ft., 14 mi. E and 25 mi. N Fairbanks, 4; Fairbanks, 2 (USBS); head of Glacier Creek, Mt. McKinley, 1 (USBS); Moose Creek, Mt. McKinley, 2 (USBS); head of Toklat River, 1 (USBS); Eagle, 4 (USBS); Yerrick Creek, 21 mi. W and 4 mi. N Tok Junction, 13; Ketchumstock, 2 (USBS); 9 mi. from mouth of Robertson River, 1 (USBS); Tanana, 3 (USBS); Tanana Crossing, 1 (USBS). Osgood (1909b:24) records specimens which may be of this subspecies from the following localities in Alaska: Charlie Creek, Circle, 20 miles above Circle, 40 miles above Circle, Nation Creek, and Seventy Mile Creek. Osgood (1900:36) also records specimens from near Fort Yukon. None of these has been seen by me; they are only tentatively assigned to this subspecies.
Microtus pennsylvanicus drummondii (Audubon and Bachman)
Arvicola drummondii Audubon and Bachman, Quadr. North Amer., 3:166, 1854. (Type, by subsequent designation, from vicinity of Jasper House, Alberta.)
Microtus pennsylvanicus drummondii Hollister, Canadian Alp. Jour., Special Number, p. 23, February 17, 1913.