Davis (The Recent Mammals of Idaho, The Caxton Printers, p. 306, April 5, 1939) and Orr (Jour. Mamm., 26:69, February 12, 1945) more recently have shown that Clethrionomys wrangeli is not a member of the rutilus group (to which C. dawsoni belongs) but is a member of the gapperi group.
Our comparisons of a series of eight topotypes of wrangeli (all in the Biological Surveys Collection) with several subspecies of Clethrionomys gapperi (including phaeus, saturatus, galei, brevicaudus, and others) reveal that the differences seen in wrangeli are of the kind and degree that serve to separate subspecies. The red-backed mouse from Wrangell Island, then, should stand as Clethrionomys gapperi wrangeli (Bailey).
Specimens examined.—Total, 31, distributed as follows: Alaska: Wrangell, Wrangell Island, 27 (19 MVZ., 8 USBS); Sergief Island at mouth of Stikine River, 4 (MVZ).
Clethrionomys gapperi solus, new subspecies
Type.—Male, adult, skin and skull, No. 74939, Biological Surveys Collection, United States National Museum; from Loring, Revillagigedo Island, Alaska; obtained on September 22, 1895, by C. P. Streator; original No. 4980.
Range.—Known only from two localities on Revillagigedo Island, Alaska.
Diagnosis.—A short-tailed, dark-colored member of the gapperi group. Dorsal stripe wide, between Chestnut and Bay (capitalized color terms after Ridgway: Color Standards and Color Nomenclature. Washington, D. C., 1912), with slight mixture of black-tipped hairs; sides and venter heavily washed with Ochraceous-Tawny. Skull flattened; rostrum proportionately short and wide; auditory bullae relatively uninflated.
Comparisons.—From topotypes of Clethrionomys gapperi wrangeli, C. g. solus differs as follows: dorsal stripe wider and slightly brighter; sides brighter; venter more heavily washed with Ochraceous-Tawny (heavy wash in all 13 C. g. solus examined; in C. g. wrangeli no wash in 11, slight wash in 16, and heavy wash in only one); nasals, alveolar extent of upper cheek-teeth and incisive foramina shorter; skull shallower when measured with tympanic bullae included; rostrum averages slightly broader.
From C. g. phaeus of the adjacent mainland, C. g. solus differs in: dorsal stripe slightly darker; ventral wash more prominent; tail shorter; skull smaller in all parts measured except that nasals are approximately the same length, auditory bullae notably smaller and teeth notably narrower.
Measurements.—External and cranial measurements of adults are shown in table 1.