not obtained from Cedar Vale itself for the habitat is not suitable
there. Numerous specimens are known from 3 mi. W Cedar Vale, _in_ Cowley
County, Kansas, all of which are assigned to _cansensis_. Osgood's
recorded locality is situated between this locality and the type
locality of _cansensis_, which is 4 mi. E Sedan, Chautauqua County,
Kansas. The distribution of _cansensis_ also is shown in Fig. 1.

[Illustration: FIG. 1. Distribution of the brush mouse in Kansas. The
southernmost row of counties includes from left to right Cowley,
Chautauqua, Montgomery, Labette, and Cherokee. Black dots represent
trapping localities from which brush mice were not obtained. Triangles
represent localities from which brush mice were obtained. The stippled
area contains suitable habitat for the brush mouse, but was not
investigated. The easternmost triangle represents a place 2 mi. S
Galena, Cherokee Co., Kansas, from which _P. b. attwateri_ is known. The
westernmost triangle represents a place 3 mi. W Cedar Vale, _in_ Cowley
Co., Kansas, from which _P. b. cansensis_ is known. The triangle of
intermediate position represents the type locality of _P. b. cansensis_,
a place 4 mi. E Sedan, Chautauqua Co., Kansas. Many of the trapping
localities have been investigated more than once.]

The probable geographic range of _P. boylii_ is based on trapping data
(see Fig. 1). The brush mouse is confined to systems of wooded cliffs in
Kansas. The two subspecies seem to be separated by more than 80 miles of
grasslands. Blair (1959) has postulated that in the northeastern part of
its range _P. b. attwateri_ is represented by disjunct, relict
populations formed by diminishing montane or cool, moist environmental
conditions. He has implied that the critical climatic change occurred
during post-Wisconsin times, and that the isolation of these populations
occurred so recently that no morphological differentiation has resulted
in them. Inasmuch as the species is widely distributed in Mexico, the
southwestern United States, and in California, and has been recorded
from the Pleistocene of California (Hay, 1927:323), it is reasonable to
suppose that the species immigrated into Kansas from the southwest and
that the immigration was in a generally northward or eastward direction.
If long tail and large eyes are specializations for a scansorial mode of
life (discussed below), then _P. b. cansensis_ must be considered more
primitive than _P. b. attwateri_ for