_Description._--Size medium; back relatively dark, near Ochraceous-Tawny with admixture of black-tipped hair; dorsal band relatively wide but not sharply defined against color of sides; side lighter than back, from near Ochraceous-Tawny to near Cinnamon and lined with black-tipped hair; lateral line distinct of clear Cinnamon-Buff or Light Ochraceous-Buff; underparts white, often suffused with Ochraceous-Buff; tail distinctly bicolored, dark brown to black above and yellowish-white to grayish-white below; ears dark, usually flecked with Tawny Ochraceous and edged with ochraceous; feet grayish-white above; incisive foramina relatively short and broad; pterygoid fossae relatively broad; auditory bullae broad and well inflated; mastoid region relatively broad; zygomata relatively short; inferior arm of zygomatic process of maxillary relatively broad. _Comparison._--From _Zapus hudsonius acadicus_, which _Z. h. ladas_ closely resembles, it differs in: Color darker, dorsal band much less distinct, underparts more frequently suffused with Ochraceous-Buff; auditory bullae relatively broader and more inflated; pterygoid fossae broader; zygomata averaging shorter; incisive foramina relatively shorter; inferior arm of zygomatic process of maxillary relatively broader. From _Zapus hudsonius canadensis_, _Z. h. ladas_ differs as follows: Color darker, more richly tawny, dorsal band less distinct; auditory bullae relatively shorter, more inflated; pterygoid fossae averaging broader; zygomata averaging broader; incisive foramina averaging longer. _Remarks._--This subspecies retains all of its diagnostic characters throughout nearly all parts of its geographic range. Specimens from Nova Scotia are like _Z. h. ladas_ in their darker color and less distinct dorsal band, but in the remainder of their characters they are distinct and best referable to _Z. h. acadicus_. _Zapus h. ladas_, with its relatively large size, poorly defined dorsal band, and broad, well inflated auditory bullae, is one of the better marked subspecies of the species _Zapus hudsonius_. _Specimens examined._--Total, 41, distributed as follows: LABRADOR: Mahkovik, 1 (USNM); Etagaulet Bay, Lake Melvikl, 2 (USNM); 3 mi. above mouth of Naskaupi River, 1 (USNM); _Northwest River_, 6, (USNM); Cartwright, 1 (USBS); Muskrat Falls, Hamilton River, 1 (USNM); Hamilton River, Flour Lake, 3 (USNM); Hawke Harbor, 4 (USNM); Goose Bay, 3 (USNM); _Niger Sound, Islet Bay_, 1 (USNM); Red Bay, 5 (USNM); _Mecklenburg Harbor_, 2 (USNM); _Mary Harbor_, 1 (USNM). NEWFOUNDLAND: Hare Harbor, 3 (USNM). _Quebec_: northwest Ungava, 1 (NMC); Moise Bay, 5 (NMC); Trout Lake, near Moise Bay, 1 (NMC). _Marginal records._--Labrador: Mahkovik; Red Bay. Newfoundland: Hare Harbor. Quebec: Trout Lake, near Moise Bay; northwest Ungava. =Zapus hudsonius pallidus= Cockrum and Baker _Zapus hudsonius pallidus_ Cockrum and Baker, Proc. Biol. Soc. Washington, 63:1, April 26, 1950.