Specimens from Minaki, Ontario, are tending toward Zapus hudsonius intermedius in lighter coloration but in the size and shape of the auditory bulla, size and shape of the incisive foramina, and in the width of the pterygoid fossae they are more nearly like Z. h. hudsonius to which they are here referred. Specimens from various localities in Menominee County, Michigan, are like Z. h. intermedius in shape of the incisive foramina and shape of the postpalatal notch, but in color of pelage, size and shape of the auditory bullae, and breadth of the pterygoid fossae they closely resemble Z. h. hudsonius.
In Wisconsin, intergradation occurs in color and in cranial characters in specimens from Mercer, Solon Spring, and in a single individual from Basswood Lake. All these specimens, however, are best referable to Z. h. hudsonius.
Specimens from one mile southwest of Fairbanks and from Fairbanks, Alaska, show intergradation with Zapus hudsonius alascensis in coloration (more brown, less black), but in small size, short, broadly rounded incisive foramina, and in size and shape of the auditory bullae are nearest to Z. h. hudsonius to which they are here assigned.
Intergradation with Zapus hudsonius alascensis is noted also in specimens from McIntyre Creek, Yukon. They are like Z. h. alascensis in the size and shape of the auditory bullae and in the more elongate incisive foramina, but in the coloration, size of the pterygoid fossae, and breadth of the braincase are more nearly like Z. h. hudsonius and are here referred to this geographic race.
In British Columbia, in specimens from 1 mi. NW junction of Irons Creek and Laird River as well as in those from Hot Springs, 3 mi. WNW junction of Trout River and Laird River, and in those from 1/4 mi. S of the junction of the same rivers, three way intergradation occurs. These animals are like Zapus hudsonius alascensis in color and in length of tail. They agree with Zapus hudsonius tenellus in shape of nasals. In degree of inflation of auditory bullae, in length and width of incisive foramina, and in shape of pterygoid fossae they are as in Z. h. hudsonius to which they are here assigned.
Specimens examined.—Total, 230, distributed as follows:
Alaska: Fairbanks, 1 (USNM); 1 mi. SW Fairbanks, 440 ft., 1.
Alberta: Conibear Lake, Wood Buffalo Park, 1 (NMC); Assineau River, 1920 ft., 10 mi. E and 1 mi. N Kinuso, 1; Mountain Rapid, Athabasca River, 1 (USBS); Brule Rapid, Athabasca River, 1 (USBS); 25 mi. above Pelican Rapid, Athabasca River, 1 (USBS); Lac la Nonne, 7 (NMC); Swift Current, Athabasca River, 1 (USBS); junction Lac la Biche River and Athabasca River, 1 (USBS); 30 mi. above Athabasca Landing, Athabasca River, 1 (USBS).
British Columbia: 1 mi. NW junction Irons Creek and Laird River, 3; Hot Springs, 3 mi. WNW junction Trout River and Laird River, 1; 1/4 mi. S junction Trout River and Laird River, 1.