Examination of specimens of _Microtus longicaudus_ from Washington east of the Cascade Range (those from the Blue Mountain area excepted) discloses that the skulls do not differ essentially from those of topotypes of _M. l. mordax_, but do differ, as outlined above, from near-topotypes of _M. l. halli_. There is considerable variation in color among the Washington-taken specimens of _Microtus longicaudus_. Animals from the eastern flanks of the Cascades average darker than those taken, north of the Snake River, still farther east in Washington. Possibly Dalquest (_op. cit._) relied mainly upon this darker color in assigning the specimens from eastern Washington to _M. l. halli_. Relying principally upon cranial characters, we conclude that most of the specimens are better referred to _M. l. mordax_ and that _M. l. halli_ is restricted, in Washington, to the Blue Mountains. _Specimens examined of Microtus longicaudus mordax._--Total, 74, all in the Biological Surveys Collection, distributed as follows: Washington: _Okanogan_ _County_: mouth of Holmar Creek, W Fork Paysaten River, 4700 ft., 1; Conconully, 3; Twisp, 1; Omak Lake, 1200 ft., 3. _Stevens County_: 5 mi. N Colville, 1. _Pend Oreille County_: 9 mi. N Metalina, 2600 ft., 1; Sullivan Lake, 3000 ft., 3. _Chelan County_: Sethekin, 1079 ft., 3; head of Lake Chelan, 900 ft., 12; Hart Lake, Railroad Creek, 3900 ft., 1; Entiat, 20 mi from mouth of Entiat River, 1680 ft., 13; Wenatchee, 4. _Douglas County_: Waterville, 1. _Jefferson County_: Cleveland, 2. _Kittitas County_: 2 mi. S Blewett Pass, 3000 ft., 6: Ellensburg, 1500 ft., 4. _Whitman County_: Colfax, 2. _Yakima County_: McAllister Meadows, Tieton River, 3000 ft., 3; Gotchen Cr., 5500 ft., near Sava Spring, Mt. Adams, 2. _Klickitat County_: 8 mi. S Glenwood, base Mt. Adams, 2. _Asotin County_: Anatone, 3300 ft., 4; Bly, 1000 ft., 2. Microtus miurus muriei (Nelson) 1931. _Microtus muriei_ Nelson, Jour. Mamm., 12:311, August 24, type from Kutuk River (tributary of Alatna River), Endicott Mts., Alaska.