For comparisons with Zapus princeps cinereus, Zapus princeps pacificus and Zapus princeps idahoensis see accounts of those subspecies.
Remarks.—The coloration in Z. p. oregonus varies somewhat from north to south. In the northern part of the range the average coloration of the upper parts is darker with more ochraceous on the sides. To the southward the upper parts are progressively paler and the sides are near Light Pinkish-Cinnamon. Because of this variation of color, and because of the small samples available to workers in the past, three populations of this subspecies have been named as distinct. However, with the large amount of additional material now available, the supposed diagnostic characters of these “forms” prove to be within the range of individual variations of each of several populations of which large samples are available.
Zapus major Preble (1899:24) was described as having zygomata short, palate broad and long, incisive foramina large and elliptical, and color dark. Some specimens of Z. p. oregonus, from nearly all parts of its geographic range, show these same characters. Resemblances in anteriorly divergent tooth-rows, broad interorbital region, small auditory bullae, and posteriorly narrow nasals, are additional reasons for placing Z. major as a synonym of Z. p. oregonus.
Zapus nevadensis Preble (1899:25), here considered a synonym of Z. p. oregonus, was described as having: auditory bullae small, posterior border of the palate usually convex anteriorly, palatal bridge long, and color pale. These characters, however, are within the range of individual variation of Zapus p. oregonus. Similarities such as tooth-rows diverging anteriorly, nasals narrow posteriorly, interorbital region broad, and incisive foramina enlarged posteriorly are added reasons for placing Z. nevadensis as a synonym of Z. p. oregonus.
Zapus princeps palatinus Hall (1931:8) was described as having: palatal bridge long, incisive foramina wide posteriorly, posterior border of palate straight or convex posteriorly, and color pale. These characteristics are to be found in some individuals in most populations of Z. p. oregonus. Additional well marked cranial similarities, such as small auditory bullae, broad interorbital region, and nasals narrow posteriorly offer additional evidence as to the close relationship of Z. p. palatinus and Z. p. oregonus. Hall (loc. cit.), with a small sample available to him for comparative purposes (14 specimens of Z. p. palatinus and 12 specimens of Z. p. nevadensis), was impressed by the condition of the palate in Z. p. palatinus and wrote: “the generally straight, or even posteriorly convex, posterior border of the palate seems to be unique among described forms of Zapus. The name palatinus is given in allusion to this structural feature.” With more than 300 specimens of Z. p. oregonus available for study I find that a straight or posteriorly convex posterior border of the palate occurs in more than 50 per cent of the individuals examined. Specimens displaying this described palatal condition are known from all parts of the range of Z. p. oregonus, but do occur in a higher percentage of specimens in the area ascribed by Hall (loc. cit.) to the range of Z. p. palatinus.
Intergradation with Zapus princeps idahoensis and Zapus princeps cinereus is discussed in the accounts of those subspecies.
Specimens examined.—Total, 340, distributed as follows:
California: Modoc Co.: Buck Creek R. S., 1 (CAS); Willow Ranch, 4 (CAS); Sugar Hill, 5000 ft., 1 (MVZ); Goose Lake Meadows, near Sugar Hill, 4 (MVZ); Parker Creek, Warner Mts., 5500 ft., 18 (MVZ); Dry Creek, Warner Mts., 4800 ft., 3 (MVZ) east face Warner Peak, Warner Mts., 8700 ft., 1 (MVZ); 5 mi. NW Eagle Peak, 7000 ft., 5 (MVZ); Lassen Creek, 1 (SDM); Happy Camp, 1 (CAS).
Idaho: Boise Co.: Bald Mtn. R. S., Boise Nat’l Forest, 10 mi. S. Idaho City, 7400 ft., 2 (USBS). Elmore Co.: Trail Creek, Boise Nat’l Forest, 2 (USBS). Washington County: 1 mi. NE Heath, SW Slope Cuddy Mtn., 4000 ft., 20 (5 MVZ).
Nevada: Elko County: 6 mi. SW Mountain City, Cobb Creek, 6500-6550 ft., 44 (MVZ); summit between heads of Copper and Coon creeks, Jarbidge Mts., 18 (9 MVZ); head of Ackler Creek, 6800 ft., 2: Steel Creek, 7000 ft., 11 (4 MVZ); summit of Secret Pass, 6200 ft., 8; south fork Long Creek, 7830 ft., 4; Harrison Pass R. S., Green Mtn., Canyon, 6050 ft., 12. Eureka County: 4 mi. S Tonkin, Denay Creek, Roberts Mt’s, 1 (MVZ). Humboldt County: Martin Creek R. S., 1 (MVZ); 13 mi. N Paradise Valley, 6700 ft., 19 (MVZ). Lander County: Kingston R. S., 7500 ft., 4 (MVZ). Nye County: Wisconsin Creek, 7000 ft., 12 (MVZ). White Pine County: Willow Creek, 2 mi. S Elko County line, Ruby Mts., 6500 ft., 24 (2 MVZ).