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.