Differences from streatori, in males, are: skull averaging larger in every cranial and dental measurement taken; 36 per cent heavier; tympanic bulla longer than, instead of about same length as, upper tooth-rows. In females the inner lobe of M1 is shorter anteroposteriorly; otherwise all measurements of fallenda average larger and it is 33 per cent heavier; rostrum and interorbital region broader in relation to remainder of skull.
In comparison with gulosa, skulls of males differ as follows: averaging larger in every measurement taken with no overlap in several dimensions; 50 per cent heavier; tympanic bullae with anterior margins projecting slightly below squamosals rather than flush with same; length of bulla more than, rather than about same as, that of upper tooth-rows. Considering the great difference in size, the relative proportions are remarkably alike. In females, length of inner lobe of M1 about the same; otherwise averaging larger in every measurement taken; 44 per cent lighter; relative to basilar length, tooth-rows longer, skull wider across zygomata and mastoids, rostrum and interorbital regions slightly narrower, skull shallower in plane of last upper molars.
Comparisons with haidarum, invicta and anguinae are made in accounts of those subspecies.
Remarks.—Until the name fallenda was proposed in the course of the present study, most of the specimens of this race were assigned to streatori.
Intergradation with streatori is complete as it is also with invicta and richardsonii, in other words with each of the subspecies whose ranges meet that of fallenda. In color and in size the difference is least between streatori and fallenda. As between fallenda and invicta the size is not greatly different and the intergradation in color is gradual. Between fallenda and richardsonii intergradation is somewhat different and to fully appreciate its nature we should remember that the color of fallenda resembles that of the saturate coastal races, streatori, anguinae and olympica although the black tip of the tail is longer. In this latter feature and in several cranial details, as well as in greater degree of secondary sexual variation in size, fallenda resembles richardsonii. Because the two differ more than do most subspecies of ermine whose ranges meet, some of the intergrades at first inspection appear to be widely different from either parent stock. For example, specimens from Alta Lake, British Columbia, may give this impression because the combination of large size and dark color suggests a kind of ermine different from either fallenda or richardsonii. In no instance, however, has there been found in these intergrades any character other than those occurring in one or the other of the two parent races.
Along the coast in the north part of the geographic range assigned to fallenda, some specimens nearly typical of richardsonii have been taken so near to the place where fairly typical fallenda was obtained that I have doubted whether there is intergradation in the usual fashion in this area; more specimens will have to be obtained from this coastal area to resolve the doubt one way or the other.
The winter pelage is brown in all specimens at most localities. The only white pelage seen was in each of three specimens from Glacier, Whatcom County, Washington. A fourth specimen from there is in brown winter pelage. At any one locality there is much variation in the degree to which the dark color of the upper parts encroaches on the area that in most other races is light-colored. An extreme degree of encroachment is shown by a specimen taken on December 1, 1935, by R. A. Cummings, at Vancouver, British Columbia, in which the light color occurs only in three restricted areas, the chin, the throat and the lower breast; otherwise the coat is brown. There are other specimens, for instance from the type locality, which differ mainly in having an additional white spot in the inguinal region. The opposite extreme, in a specimen also from the type locality, is where the least width of the light-colored underparts on the abdominal region is a third of the circumference of the body. The two extremes are connected by a dozen intermediate stages. Of 64 specimens in which the color of the lips was carefully examined, one, from Vancouver, has both the upper and lower-lips brown; 9 have both the upper and lower-lips white; and 54 have the upper lips brown and the lower lips white.
Specimens examined.—Total number, 72, arranged by localities from north to south. Unless otherwise indicated, specimens are in the National Museum of Canada.
British Columbia. Horseshoe Lake, Stillwater, 2; Vancouver, 1[74]; Point Grey, 1[31]; Port Moody, 5[91]; Chilliwack, 8 (2[75], 4[91], 1[60]); Sumas, 19 (18[75], 1[60]); Thurstons Ranch, 2; Cultus Lake, 2; Mt. Baker Range, 5[75]; Lihumption Park, 1; Huntingdon, 14; Tami Hy Creek, 1.
Washington. Whatcom County: Semiahmoo, 1[91]; New Whatcom, 1[68]; Lake Whatcom, 2[91]; 5 mi. W Glacier, 1[51]; Glacier (3 at 900 ft.), 4[91]; E Side Easton Glacier, Mt. Baker, 1[55]; Morovitz Guard Station, 831 ft., 1[55].