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.