Co.: Hot-springs Cr., 4. Lake Co.: end of W arm Flathead Lake, 5; Ravalli, 8. Ravalli Co.: Florence, 2; 8 mi. NE Stevensville, 4000 ft., 1; Corvallis, 4; 6 mi. E Hamilton, 3700 ft., 2(K.U.).

Comparative materials (in U.S. Nat. Mus., Biol. Surv. Coll.).—Microtus montanus nanus: Total, 72, as follows: IDAHO: Lewis Co.: Nez Perce, 3. Idaho Co.: Seven Devils Mts., 3550 ft., 3. Custer Co.: Challis, 7; Pahsimeroi Mts. (9300 ft., 8; 9700 ft., 4), 12. Butte Co.: Lost River Mts., 1. Canyon Co.: Nampa, 1; Bowmont, 1. Ada Co.: Boise, 1. Blaine Co.: Sawtooth Lake, 2; Alturas Lake, 3. Owyhee Co.: Three Cr., 3. Minidoka Co.: Heyburn, 2. Bannock Co.: Pocatello, 4. Bear Lake Co.: Montpelier Cr., 3. MONTANA: Fergus Co.: Big Snowy Mts., 11. Gallatin Co.: West Fork of West Fork, Gallatin River, 1. Park Co.: Lamar River, 7000 ft., 2; Gardiner, 1. Sweetgrass Co.: "near" head Big Timber Cr., Crazy Mts., 1; Big Timber Cr., 5200 ft., Crazy Mts., 1; 14 mi. S Big Timber, 1; West Boulder Cr., 18 mi. SE Livingston, 2; McLeod, 1. Carbon Co.: Beartooth Mts., 2; Beartooth Lake, 1. WYOMING: Park Co.: N end Lake, Yellowstone Nat'l Park, 2.

Microtus montanus canicaudus Miller

1897. Microtus canicaudus Miller, Proc. Biol. Soc. Washington, 11:67, April 21, type from McCoy, Willamette Valley, Polk County, Oregon.

In 1938 when one of us (Hall, Proc. Biol. Soc. Washington, 51:131–134, August 23, 1938) arranged several nominal species of Microtus as subspecies of the species Microtus montanus, Microtus canicaudus was not included because that writer had not examined representative specimens. In the U.S. Biological Surveys collection in the U.S. National Museum we have examined specimens of M. m. canicaudus, all from Oregon, as follows: Hood River (Catalogue Nos. 262583–262586); Canby (262577, 262578); Wapinitia (79985–79988); Sheridan (69779, 69780); McCoy (75834–75842, 77744); Salem (246736); Albany (161554); and Corvallis (242552). The four specimens from Wapinitia seem to be those that Bailey (N. Amer. Fauna, 17:29, June 6, 1900) listed as Microtus montanus. The diagnostic characters mentioned by Miller in the original description (Proc. Biol. Soc. Washington, 11:67, April 21, 1897) included the following: size approximately the same as in Microtus [montanus] nanus; upper parts yellowish; tail usually nearly uniform grayish above and below; auditory bullae much inflated; lateral pits at posterior edge of bony palate unusually shallow. Because the tails of the original series were understuffed and variously rotated, they seemed to be less sharply bicolored than is the case, as shown by subsequently collected specimens. Otherwise we find that the characters mentioned above differentiate canicaudus from its nearest relatives, Microtus montanus canescens to the northward, M. m. nanus to the eastward, and M. m. montanus to the southward. In canicaudus we have noted one additional differential character; the interpterygoid space is acuminate anteriorly. In this feature and in each of the other features mentioned above, intergradation with Microtus montanus nanus is seen in the specimens from Hood River and Wapinitia. In the specimens from Hood River the auditory bullae are only slightly less inflated than in those topotypes of canicaudus having the smallest bullae; there is appreciable variation in size of the bullae in the topotypes. Even so, the minimum size of bullae among the topotypes is larger than the maximum size in the specimens from Wapinitia. The four specimens from Wapinitia have the yellowish color of canicaudus to a considerable degree, and show intergradation between canicaudus and nanus in depth of the palatal pits and shape of interpterygoid