Specimens examined.—Total 93, as follows: Yukon Territory: McIntyre Creek, 2250 ft., 3 mi. NW Whitehorse, 26; W side Lewes River, 2150 ft., 2 mi. S Whitehorse, 4; 5 mi. W Teslin River, 2400 ft., 16 mi. S and 53 mi. E Whitehorse, 7; E side Teslin River, 2300 ft., 16 mi. S and 59 mi. E Whitehorse, 1. British Columbia: 1 mi. NW jct. Irons Creek and Liard River, 8; Hot Springs, 3 mi. WNW jct. Trout River and Liard River, 3; N side Liard River, ½ mi. W jct. Liard River and Trout River, 1; ¼ mi. S jct. Trout River and Liard River, 13; S side Toad River, 10 mi. S and 21 mi. E Muncho Lake, 2; Summit Pass, 4200 ft., 10 mi. S and 70 mi. W Fort Nelson, 2; E side Minaker River, 1 mi. W Trutch, 19; Beatton River, 115 mi. S Fort Nelson, 1; 5 mi. W and 3 mi. N Fort St. John, 2. Alberta: Assineau River, 1920 ft., 10 mi. E and 1 mi. N Kinuso, 4.
Remarks.—Adults among the specimens listed above vary but little; one female from Assineau River in Alberta is notably more reddish than others taken elsewhere.
Average and extreme measurements of nine adults of both sexes of M. p. drummondii from E side Minaker River, 1 mi. W Trutch, British Columbia, are as follows: Total length, 157 (148-165); length of tail, 42 (37-46); condylobasal length, 25.1 (24.7-26.0); basal length, 24.2 (23.4-25.0); length of nasals, 6.8 (6.4-7.2); zygomatic breadth, 14.4 (13.9-14.7); breadth across auditory bullae, 12.4 (12.0-12.7); alveolar length of upper molariform tooth-row, 6.1 (6.0-6.2); Nine adults of both sexes from McIntyre Creek, 2250 ft., 3 miles northwest of Whitehorse, Yukon Territory, have the following measurements: 153 (147-168); 40 (33-47); 24.9 (24.2-25.5); 24.0 (23.6-24.6); 6.6 (6.2-7.2); 14.4 (13.9-15.1); 12.1 (11.7-12.5); 6.1 (6.0-6.2).
Microtus cf. cantator Anderson
Yukon Singing Mouse
Microtus cantator Anderson, Nat. Mus. Canada, Bull. No. 102, Biol. Ser. No. 31:161, [for 1946], January 24, 1947. (Type "taken in tundra-slide above timber-line on mountain top near Tepee Lake on north slope of St. Elias Range," Yukon Territory, Canada.)
Specimen examined.—One from Alaska: Fish Creek, 3400 ft., 5 mi. N and 1 mi. E Paxson.
Remarks.—The single adult male, obtained by Alcorn, has been compared by Dr. Henry W. Setzer with specimens of Microtus muriei Nelson, M. miurus miurus Osgood, and M. m. oreas Osgood in the United States National Museum. He reports that the specimen is related most closely to M. miurus but exhibits characters by which it is, at least, subspecifically distinct from these two forms of this species. Three specimens of M. andersoni Rand and one of M. cantator Anderson, borrowed from the National Museum of Canada are less mature than the specimen in question. Even so, the male from Fish Creek is less gray than M. andersoni and as seen from measurements of the type, an adult male (Rand, 1945:42), is larger with longer tail and has a shorter and narrower skull and is judged to be taxonomically separable. M. cantator was named from two specimens; both the paratype (seen by me) and seemingly the type are too young to show clearly subspecific characters. Alcorn's specimen is tentatively referred to M. cantator until some adult topotypes can be obtained. Measurements of the male, No. 21539, from Fish Creek, are: Total length, 152; length of tail, 30; hind foot, 22; condylobasal length, 28.0; basal length, 26.6; length of nasals, 7.1; zygomatic breadth, 13.8; breadth across auditory bullae, 11.5; least interorbital breadth, 3.3; alveolar length of upper molariform tooth-row, 6.2.
Alcorn took this specimen in an area above timberline where a low growth of willow was the dominant vegetation. Traps were set where he had seen a mouse go into a small burrow. The next morning, August 18, 1947, he found this specimen and two Microtus oeconomus macfarlani in his traps.
Microtines of the subgenus Stenocranius from continental areas of Alaska and Northwestern Canada are represented in collections by a few specimens from widely separated localities. Lacking material from intermediate localities, describers have given specific recognition to several of these isolated populations. Future collecting will be necessary to disclose whether the North American mice of this subgenus belong to one or to more than one species and may disclose whether or not there has been more than one invasion of the North American continent by members of this Asiatic group.