Part 13

Embryos in 25 pregnant females averaged 5 (2-7). The mammae of the female are arranged in four pairs (two abdominal, one pectoral, and one inguinal).

Z. princeps builds a grass nest on the ground which is placed under cover of vegetation or surface litter. Bailey (1932:227) writes that in New Mexico jumping mice of this species use fibers of grass to construct a ball-shaped nest. The nest usually has one opening but sometimes there are two. In the Ruby Mountains, of Nevada, Borell and Ellis (1934:37) found the globular nests of this mouse on the ground in tall grass.

=Zapus princeps cinereus= Hall

Zapus princeps cinereus Hall, Univ. California Publ. Zool., 37:7, April 10, 1931.

Type.--Female, adult, skin and skull; No. 45422, Mus. Vert. Zool.; Pine Canyon, 6600 feet altitude, Raft River Mountains, 17 mi. northwest Kelton, Boxelder County, Utah; obtained on July 14, 1930, by Annie M. Alexander; original No. 689.

Range.--Raft River Mt's in northwestern Utah and in isolated mountains in southern Idaho. See fig. 46. Zonal range: Transition and Canadian.

Description.--Size, medium; back with broad mid-dorsal band, varying from pale brown mixed with Pinkish-Buff to dark brown mixed with Warm Buff or Ochraceous-Buff; sides varying from near Pinkish-Buff to near Ochraceous-Buff; ventral surface white to base of hairs, not suffused with other color; tail bicolored, pale brown above and white to yellowish-white below; ears dark, edged with white or yellowish-white; upper teeth divergent anteriorly; auditory bullae small; skull relatively long; zygomata relatively weak and not widely bowed; nasals wide posteriorly; pterygoid fossae relatively narrow.

Comparisons.--From Zapus princeps nevadensis, Z. p. cinereus differs as follows: Size averaging smaller; entire coloration lighter; zygomata not so widely bowed; incisive foramina not so wide posteriorly; auditory bullae smaller; nasals wider posteriorly; pterygoid fossae narrower.

From Zapus princeps idahoensis, Z. p. cinereus can be distinguished by: generally paler color; smaller auditory bullae; broader interorbital region; anteriorly diverging tooth-rows; narrower pterygoid fossae.

For comparison with Zapus princeps utahensis see account of that subspecies.

Remarks.--Davis (1939:343) writes that "since cinereus was described from nine specimens, only two of which are near adult, one cannot place much value on the coloration ascribed to it by Hall (1931:7)." I examined the type series and found, as did Davis (loc. cit.), that the type is much lighter and grayer than is a near adult paratype, which was obtained the same day; however, I do not concur with Davis (loc. cit.) that specimens from Mt. Harrison, 10 mi. S Albion, Idaho, which are darker and much more ochraceous than the paratype, necessarily are more nearly typically colored. These individuals, judged by cranial characters, are more nearly typical of cinereus but show intergradation with Z. p. idahoensis in their darker and more ochraceous pelage.

Durrant (1952:387) found that the gray color of Z. p. cinereus was not diagnostic in separating Z. p. cinereus from Z. p. utahensis, because gray animals are also found in Z. p. utahensis. Specimens from Camp Tendoy, Pocatello, Idaho, are intermediate in color and in cranial characters as between Z. p. idahoensis and Z. p. cinereus, but here are referred to Z. p. cinereus. Whitlow and Hall (1933:268) compared these individuals with specimens of Z. p. princeps and Z. p. cinereus, finding them intermediate but in the aggregate of several differential characters better referred to the latter.

Specimens examined.--Total, 35, distributed as follows:

IDAHO: Bannock County: Camp Tendoy, Pocatello, 2 (MVZ). Cassia County: Mt. Harrison, 10 mi. S Albion, 16 (MVZ).

UTAH: Boxelder Co.: south fork of George Creek, 5 mi. SE Yost, Raft River Mts., 6700 ft., 1 (UU); George Creek, 7 mi. SE Yost, Raft River Mts., 6500 ft., 6 (UU); Pine Canyon, 6600 ft., 17 mi. NW Kelton, Raft River Mts., 8 (MVZ); Pine Creek, 3 mi. N Rosette, Raft River Mts., 6100 ft., 2 (UU).

Marginal records.--Idaho: Camp Tendoy, Pocatello. Utah: Pine Creek, 3 mi. N Rosette, Raft River Mts., 6100 ft. Idaho: Mt. Harrison, 10 mi. S Albion.

=Zapus princeps curtatus= Hall

Zapus princeps curtatus Hall, Univ. California Publ. Zool., 37:7, April 10, 1931.

Zapus princeps oregonus, Taylor, Univ. California Publ. Zool., 7:281, June 24, 1911.

Type.--Female, adult, skin and skull, No. 7991, Mus. Vert. Zool.; head of Big Creek, 8000 feet altitude, Pine Forest Mountains, Humboldt County, Nevada; obtained on June 30, 1909, by Walter P. Taylor and C. H. Richardson, original No. 777 of W. P. T.

Range.--Pine Forest Mt's, Humboldt County, Nevada. See fig. 46. Zonal range: Transition and Canadian.

Description.--Size medium; back pale near Light Ochraceous-Buff with admixture of black hair forming dark dorsal band; sides lighter than back; lateral line faintly indicated; ventral surface white; tail bicolored, grayish-white to yellowish-white below and pale brown above; ears dark, edged with yellowish-white; feet grayish-white above; palatal bridge short; tooth-rows almost parallel; mastoid region of skull relatively narrow; incisive foramina wide posteriorly; narrow across zygomata; nasals relatively narrow posteriorly.

Comparisons.--For comparison with Zapus princeps oregonus see account of that subspecies.

Remarks.--This jumping mouse, which was described from the Pine Forest Mountains, closely resembles Zapus princeps oregonus but differs in lighter color, slightly smaller body, less divergent tooth-rows, shorter palate, and narrower skull across the mastoid region.

The Pine Forest Mountains are isolated from neighboring boreal regions by a belt of the Upper Sonoran Life-zone, which is inhospitable to Zapus; therefore, intergrades between Z. p. oregonus and Z. p. curtatus are not known and probably do not exist. Nevertheless, Z. p. curtatus shows close affinity with Z. p. oregonus, as indicated by Taylor (1911:281), and I agree with Hall (1931:7) that the relationships of Z. p. curtatus are best expressed by arranging it as a subspecies of Zapus princeps.

Specimens examined.--Total, 18, all from Nevada, distributed as follows: Humboldt County: Pine Forest Mts.; Alder Creek, 6000 ft., 2 (MVZ); head of Big Creek, 8000 ft., 14 (MVZ); Leonard Creek, 6500 ft., 2 (MVZ); Meadow, 1 (MVZ).

Marginal records.--Nevada: Pine Forest Mts., Alder Creek; Meadow.

=Zapus princeps idahoensis= Davis