ies are fairly
pronounced. Its range is isolated and widely separated from that of
any other members of the genus by open prairie country and a wide belt
of the Transition zone. There seems to be no valid reason for
considering it a subspecies."

Additional specimens have been taken in recent years from the Black
Hills of South Dakota and northeastern Wyoming. This material has shed
light on the relationships and morphological characteristics of the
red-backed mice of this region. Bole and Moulthrop (Sci. Publ.
Cleveland Mus. Nat. Hist., 5:153, September 11, 1942) listed, as
comparative material, eight specimens from Bull Springs, Custer
County, South Dakota, under the name _Clethrionomys gapperi
brevicaudus_ (Merriam). They gave no reason for arranging
_brevicaudus_ as a subspecies of _C. gapperi_.

Twenty adults (11 skins and skulls, 9 skulls only) from Pennington
County, South Dakota (specimens in the University of Michigan
Museum of Zoology), have the following measurements (averages of
external measurements based on 11 specimens only): Total length, 142
(123-155); tail, 35 (30-39); hind foot, 19.5 (18.6-21.0); basal
length, 23.3 (21.7-24.5); condylobasilar length, 23.3 (21.9-24.5);
zygomatic breadth, 13.7 (12.9-14.7); lambdoidal breadth, 11.7
(11.3-12.9); alveolar length upper cheek-teeth, 5.5 (5.2-5.8);
interorbital breadth, 3.9 (3.6-4.1); length of nasals, 7.7 (7.1-8.5);
breadth of rostrum, 3.2 (2.9-3.6); and length of incisive foramina,
5.0 (4.6-5.3).

Measurements of the type and one "more fully adult topotype" (as given
by Bailey, _op. cit._) are: Total length, 125, 130; tail length, 31,
32; hind foot, 19, 19; basal length, 21.2, 21.8; length of nasals,
6.6, 7.0; zygomatic breadth, 12.5, 12.8; mastoid breadth, 11.3, 11.0;
alveolar length of upper molar series, 5.4, 5.3. In every measurement
the figures for Bailey's specimens are smaller than the average of the
same measurement in the 20 adults from Pennington County, and, in most
measurements, are even lower than the minimum of the latter series.
Therefore, we conclude that the material available to Merriam (_op.
cit._) and Bailey (_op. cit._) consisted of only subadults.

In comparison with a series of 23 adult _Clethrionomys gapperi galei_
from 28 mi. E Lovell, Big Horn County, Wyoming, _C. g. brevicaudus_
has a slightly shorter tail, longer hind foot, greater basal and
condylobasilar lengths, greater zygomatic and lambdoidal breadths and
conspicuously