_Comparisons._--From _Zapus hudsonius alascensis_, _Z. h. hudsonius_ differs as follows: upper parts generally darker, more black tipped hair; sides darker with greater suffusion of dark hair; lateral line brighter, more distinct; size averaging smaller; zygomatic arches less bowed outward; distance from incisors to postpalatal notch shorter; zygomata shorter; occipitonasal length less; mastoid region narrower.
From _Zapus hudsonius intermedius_, _Z. h. hudsonius_ differs in: color darker, more tawny dorsally; sides averaging darker, more black-tipped hairs; size averaging larger; braincase averaging broader; distance from incisors to postpalatal notch averaging slightly shorter; zygomata averaging longer; mastoid region averaging broader; incisive foramina averaging shorter.
From _Zapus hudsonius tenellus_, _Z. h. hudsonius_ differs as follows: upper parts averaging darker; tail averaging shorter; condylobasal length averaging more; braincase averaging broader; auditory bullae broader and less inflated; interparietal averaging broader; incisive foramina more broadly rounded and averaging longer.
For comparison with _Zapus hudsonius canadensis_ and _Zapus hudsonius campestris_ see accounts of those subspecies.
_Remarks._--Preble (1899:16) had available for study five specimens of _Zapus hudsonius hudsonius_ from Hudson Bay. Four were preserved in alcohol and one as an incomplete skin (prepared from an alcoholic specimen). All were unreliable for comparative purposes owing to the effects of the preservative. Preble, therefore, (_loc. cit._) selected as a fairly typical sample a series of specimens from Tower, St. Louis County, Minnesota; these formed the basis of comparison between _Z. h. hudsonius_ and other subspecies of _Zapus hudsonius_. Now that additional material (well prepared skins and skulls) is available from the Hudson Bay region and from other localities in northern and western Canada it is evident that the specimens from Tower, although here considered to be _Z. h. hudsonius_, are not typical _Z. h. hudsonius_ but are intergrades between _hudsonius_ and specimens of _Zapus hudsonius intermedius_. Comparisons made in the present account are based on specimens from the vicinity of Hudson Bay (Fort Severen, Ontario, York Factory, Shamatawa River, and Robinson Portage, Manitoba). These individuals are considered typical of this subspecies. With these new data available the range of _Z. h. hudsonius_ is now understood to include all of the region from eastern Alaska to the northern parts of Minnesota, Wisconsin, and Michigan.