As compared with the skull of M. f. nevadensis that of effera seems, on the average, to have the preorbital part relatively smaller. Otherwise, the skull is a miniature of the skull of nevadensis, averaging about eight per cent smaller in linear measurements and weighs twenty-two per cent less. Comparisons of the skull with those of M. f. washingtoni and M. f. oregonensis are made in accounts of those subspecies.
Remarks.—This geographic race has long borne the name of Mustela arizonensis (Mearns). Small size differentiates effera from nevadensis and specimens have been allocated to one or the other subspecies on the basis of size, or average size when several individuals are available from one locality. Complete intergradation with each adjoining subspecies is indicated by numerous specimens, more of which are assigned to these adjoining subspecies than to effera itself.
The minimum of size in M. f. effera is found in the Blue Mountain region of northeastern Oregon. Specimens from the area intervening between these mountains and the Cascades average larger but are nearer the mean of typical effera than they are to the means of washingtoni, oregonensis or nevadensis.
Two males, nos. 204883, adult, and 204884, young, from Sisters, Oregon, near the eastern base of the Cascades, show approach structurally to M. f. washingtoni as it is represented at the nearby locality, Permilia Lake, at the west base of Mount Jefferson. Everything considered, however, the two specimens from Sisters are nearer to effera. A male from Condon, Oregon, shows approach to the Cascade race in slightly increased size.
No perfect skulls of adult females are available from the part of northwestern Oregon in which effera reaches its typical state of development as judged by the small size of the skull of the adult male. Skulls of adult females are available, however, from more nearly marginal localities. These, though smaller than in nevadensis, show relatively less difference in size when compared with nevadensis than do skulls of males. Even so the females at these marginal localities are smaller than those of nevadensis of comparable age and adequate material of adult female effera from the region where the males attain their extreme of small size probably will show about the same relative difference in size between nevadensis and effera as is known to exist between the adult males of these two subspecies. The small size of a subadult female, no 74631, U. S. Nat. Mus., from Asotin, Washington, constitutes partial basis for this opinion.
Of 14 adults examined none showed malformation of the frontal sinuses due to infestation by parasites.
Specimens examined.—Total number, 53, arranged within each state by counties from north to south. Unless otherwise indicated specimens are in the collection of the United States National Museum.
Oregon. Wasco County: 4 mi. S The Dalles, 1[74]; Wapinita, 1; Antelope, 2; 7 mi. E Antelope, 5. Gilliam County: Condon, 1[46]. Morrow County: 10 mi. S Hardman, 1. Umatilla County: Umatilla, 2; 15 mi. E Ukiah, 4000 ft., 1[49]. Union County: Elgin, 1; 20 mi. E Lehman, 1[46]. Wallowa County: Horse Creek, 15 mi. N Paradise, 1; Enterprise, 1[46]; Wallowa Lake, 1[46]; Wallowa Mts., 8300 ft., 1. Baker County: Haines, 1[49]; Anthony, 3[2]; Bourne, 2. Grant County: Long Creek, 1[46]; Canyon Creek, 1[46]; Strawberry Mts., 2; Silvies, 1[14]. Crook County: Prineville, 4. Deschutes County: Sisters, 2; Bend, 1. Lake County: 3 mi. W Stauffer, 1; Fort Rock, 1[46]. Harney County: 25 mi. NW Burns, 1. Malheur County: 4000 ft., Ironside, 2[2]; 1-1/2 mi. S Vale, 2.
Washington. Walla Walla County: Prescott, 4 (2[76], 1[60], 1[74]); Ft. Walla Walla, 2 (1[75]); Wallula, 1[76]. Asotin County: Asotin, 1.
Mustela frenata washingtoni (Merriam)
Long-tailed Weasel