Female (based on 4 adults): See measurements and plates 34-36; weight, 2.2 (2.2-2.3) grams; basilar length, 38.1 (37.8-39.7); zygomatic breadth more or less (less in three of four specimens) than distance between condylar foramen and M1 or than between anterior palatine foramen and anterior margin of tympanic bulla; relation of postorbital breadth to other measurements in doubt because of malformation of frontal sinuses by parasites; least width of palate not less than greatest length of P4; tympanic bulla as far posterior to foramen ovale as width of 3-1/2 to 5-1/2 upper incisors; height of tympanic bulla more than distance from its anterior margin to foramen ovale; length of tympanic bulla more than length of lower molar and premolar tooth-row and longer or shorter than rostrum. Compared with the skull of _M. f. washingtoni_ that of each sex of _altifrontalis_ averages slightly larger in every measurement taken, except measurements of teeth which are approximately the same, and is relatively deeper through the frontal region and through the braincase as measured at the anterior margin of the basioccipital. Skulls of females of _altifrontalis_ have a relatively broader interorbital region. Skulls of males of _altifrontalis_ further differ in having relatively, as well as actually, longer tympanic bullae, relatively lesser orbitonasal length and a greater relative breadth across the mastoids and across zygomata. Compared with _M. f. nevadensis_, the skull of the male of _altifrontalis_ averages slightly larger and heavier although the skulls of females are of approximately the same size and weight. Relative to the basilar length, the skulls of both sexes are deeper through the braincase and narrower across the mastoids; the rostrum is broader, especially in males; the tooth-rows are shorter and the interorbital breadth less, especially in females. Comparison with the skull of _oregonensis_ is made in the account of that subspecies. _Remarks._--Until the present study was begun, animals of this race have gone under the name _Mustela saturata_ (Merriam). The United States National Museum has a juvenile taken, in 1858, by Wayne at Astoria, O. T.; the Samuel N. Rhoads collection contained one specimen taken in 1891, at Tacoma, Washington; one in the Bangs' collection was taken at Chilliwack, British Columbia, in 1895, and the Field Museum has one taken on the Olympic Peninsula in 1898. The best material is that collected by Alex Walker, at Tillamook, Oregon.