Several adults were available from many of the localities of occurrence of _M. p. alcorni_. At the locality 9 miles west and 4 miles north of Haines, there were four which were considered to be old adults. These four had larger measurements than others considered to be fully adult. In addition, the skulls were larger and more rugged. There were occasionally old adults in other series. For the sake of uniformity, I have not considered these aforementioned old adults in the comparative studies of younger adults. This subspecies is named in honor of J(oseph). R(aymond). Alcorn, the collector.
_Measurements._--Average and extreme measurements of six adults of both sexes of _M. p. alcorni_ from the type locality are as follows: Total length, 162 (149-172); length of tail, 43 (39-45); condylobasal length, 26.3 (25.6-26.3); basal length, 25.2 (24.2-25.9); length of nasals, 7.3 (6.9-7.5); zygomatic breadth, 15.3 (14.9-15.6); breadth across auditory bullae, 12.8 (12.4-13.2); alveolar length of upper molariform tooth-row, 6.4 (6.1-6.7). Seven adults of both sexes from 9 miles west and 4 miles north of Haines have the following measurements: 158 (148-165); 45 (41-50); 26.1 (25.5-26.8); 24.8 (24.4-25.7); 7.3 (7.0-7.6); 14.9 (14.3-15.1); 12.2 (11.8-13.0); 6.2 (5.9-6.3).
_Specimens examined._--Total 65, distributed by localities of capture as follows and deposited in the University of Kansas Museum of Natural History: _Alaska_: E side Deadman Lake, 1800 ft., 15 mi. SE Northway, 7; 1 mi. NE Anchorage, 100 ft., 1; Tyonek, Cook's Inlet, 1; E side Chilkat River, 100 ft., 9 mi. W and 4 mi. N Haines, 37. _Yukon Territory_: 6 mi. SW Kluane, 2250 ft., 14; SW end Dezadeash Lake, 2; 1½ mi. S and 3 mi. E Dalton Post, 2500 ft., 3. Specimens reported by Osgood (1904:35) have not been seen by me but may be of this subspecies, and are tentatively referred to it. These are from the following localities in Alaska: Lake Clark near Keejik, near the mouth of the Chulitna River, and Kakhtul River near the junction with the Malchatna.
Microtus pennsylvanicus tananaensis new subspecies
_Type._--Female, adult, skin with skull, No. 21509, Univ. Kansas, Mus. Nat. Hist., Yerrick Creek, 21 mi. W and 4 mi. N Tok Junction, Alaska; 20 July 1947; obtained by J. R. Alcorn; original No. 5023.