Intergradation with _Zapus princeps oregonus_ was noted by Davis (1939:340) in a specimen from Cedar Mountain in Idaho. I have not seen this individual which he referred to _Z. p. idahoensis_ but have seen a specimen from the N Fork of Potlatch River (15 mi. SE Cedar Mt.), which, in color, closely resembles _Z. p. oregonus_ but cranially (shape of incisive foramina, size, and inflation of auditory bullae) is more nearly like _Z. p. idahoensis_ to which it is referred. Davis (_loc. cit._) indicates that specimens from summit of Smith Mt., from 1 mi. N Bear Creek R. S., from 1/2 mi. E Black Lake, and from 3 mi. W Payette Lake, Idaho, are in an area of intergradation between _Z. p. oregonus_ and _Z. p. idahoensis_, but he referred them to _Z. p. idahoensis_ on the basis of cranial characters and length of hind foot. Seven specimens from Alturas Lake, 7000 ft., Idaho, were likewise so allocated by Davis (_loc. cit._). I concur with him and in addition refer the following intermediate individuals from Idaho to _Z. p. idahoensis_: New Meadow, 1; Warren, 1; Perkins Lake, 7000 ft., Sawtooth Nat'l Forest, 1; Prairie Creek, 12 mi. W Ketchum, 2400 ft., 3. All are more nearly like _Z. p. oregonus_ in color but cranially they show more resemblance to _Z. p. idahoensis_. In the eastern part of the range of _Z. p. idahoensis_, intergradation occurs with _Zapus princeps minor_, as at 15 mi. S Heath, N Fork Flat Willow Creek, Big Snowy Mt's, Montana. Specimens from there have the lateral line enlarged and the maximum seen in this species of Ochraceous color ventrally. The pterygoid fossae are large and the bullae are reduced as in _Z. p. minor_, but in the sum total of the characters the mice more closely resemble _Z. p. idahoensis_. At Lewistown, 7 mi. NE Judith Mt's, Lime Kiln Gulch, Montana, the animals are colored as are _Z. p. minor_ but cranially are like _Z. p. idahoensis_ to which they are referred. Specimens from the Highwood Mt's, Montana, also are intergrades; they have a relatively distinct lateral line as in _Z. p. minor_ but show no ventral suffusion of Ochraceous; they have large bullae, nasals that are straight in lateral profile and other cranial characters of _Z. p. idahoensis_ to which they are here referred. A single specimen from Kamiak Butte, Whitman County, Washington, has been referred to _Z. p. idahoensis_ by Dalquest (1948:373). I have not seen this individual, but, on geographic grounds, it is likely to be of this subspecies. _Specimens examined._--Total, 342, distributed as follows: ALBERTA: Boom Creek, 5600 ft., 27 mi. W Banff, 2 (NMC); _Banff, Cascade Basin_, 2 (NMC); _Bryant Creek, Banff Park_, 1 (NMC); _Spray River, 7 mi. Cabin, Banff Park_, 3 (NMC); Crows Nest Pass, 2 (NMC); Waterton Lakes Park, 16 (NMC); _Linnets Pond, Waterton Lakes Park_, 4 (NMC); _Bertha Creek, Waterton Lakes Park_, 8 (NMC).