Zapus hudsonius intermedius new subspecies
Type.—Male, adult, No. 83400, Univ. Michigan Mus. Zool.; Ridgeway, Winneshiek County, Iowa; obtained on July 22, 1939, by S. A. Hoslett, original No. 517.
Range.—Eastern Montana, North Dakota, probably northern South Dakota, all but northern parts of Minnesota and Wisconsin, Iowa, Illinois, southwestern Indiana, and western Kentucky. See [fig. 47]. Zonal range: Upper Austral (Upper Sonoran and Carolinian) and Transition (Alleghanian and Transition).
Description.—Size medium; back from near Warm Buff to near Ochraceous-Buff with admixture of hair tipped with black or dark brown usually forming distinct, broad, dorsal band; sides lighter, from near Warm Buff to near Ochraceous-Buff with sparse mixture of dark-tipped hairs; lateral line often poorly marked but when present of clear Ochraceous-Buff; belly white, sometimes with slight suffusion of color of sides; tail bicolored, grayish-brown to brownish-black above, white to grayish-white or yellowish-white below; ears dark, narrowly edged with color of sides; feet white to grayish-white above; tail relatively short; lateral margins of nasals parallel; auditory bullae relatively short, broadly rounded, and moderately inflated; incisive foramina relatively long and narrow; pterygoid fossae relatively narrow; zygomata relatively long; inferior ramus of zygomatic process of maxillary frequently lacking a median projection.
Comparisons.—From Zapus hudsonius pallidus, Z. h. intermedius differs as follows: Coloration duller, not so bright, more yellow or buff and less bright Ochraceous-Buff; interorbital region averaging narrower; incisive foramina averaging longer and narrower; condylobasal length averaging greater; braincase averaging broader; mastoid region averaging broader.
For comparisons with Zapus hudsonius hudsonius, Zapus hudsonius campestris, and Zapus hudsonius americanus see accounts of those subspecies.
Remarks.—Zapus hudsonius intermedius has a large geographic range. There is some variation detectable when individuals from widely separate localities are compared, but where there is much variation it is obviously the result of intergradation. All characters differentiating Z. h. intermedius from any contiguous subspecies are not present in every specimen even in the type series. Nevertheless, a certain series of cranial characters (narrow incisive foramina, short rounded auditory bullae, parallel lateral margins of nasals and narrow pterygoid fossae) is diagnostic.
Animals obtained from extreme southwestern Indiana and from eastern Illinois approach Z. h. americanus in color and in shape of the incisive foramina, but in the shape of the nasals, width of the pterygoid fossae and breadth of the zygomata are most nearly like Z. h. intermedius to which they are here referred. Specimens from Lake and Kane counties, Illinois, also show affinity with Z. h. americanus in color, but cranially are most nearly like Z. h. intermedius and are assigned to that subspecies.
Two specimens from southern Illinois (Perry County) are intergrades between Z. h. pallidus and Z. h. intermedius. Cockrum and Baker (1950:3) mentioned that these individuals showed evidence of intergradation with Z. h. pallidus in color of the pelage and the breadth of the least interorbital constriction. In other characters the specimens are most nearly like Z. h. intermedius to which they are here referred. Animals from Lyon County, Iowa, also show intergradation between Z. h. pallidus and Z. h. intermedius. These individuals are most nearly like Z. h. pallidus in interorbital breadth of the skull but in other characters agree with Z. h. intermedius and, therefore, are referred to that subspecies.
Intergradation between Z. h. campestris and Z. h. intermedius is noted in a specimen from 7 mi. NE Glendive, Montana. This individual has the larger, broader, auditory bullae and more widely bowed incisive foramina of Z. h. campestris, but in color, in smaller external size, and in the majority of cranial characters it is best referred to Z. h. intermedius.