ological Surveys
Collection, United States National Museum; from Little Colorado River,
8300 ft., White Mountains, Apache County, Arizona; obtained September
12, 1908, by C. Birdseye, original number 152.

_Range._--Known only from the White Mountains of eastern Arizona.

_Diagnosis._--Dorsal stripe near Chestnut, with an underwash of
between Tawny and Russet, and a mixture of black-tipped hairs,
resulting in an overall effect of near Chestnut. Skull wide across
zygomatic arches and narrow across mastoids; rostrum narrow and
posterior border of palate straight.

_Comparisons._--This subspecies needs close comparison only with the
adjacent subspecies _C. g. limitis_. As compared with topotypes of
_limitis_, _C. g. arizonensis_ has darker pelage, narrower rostrum,
greater width across zygomatic arches, lesser lambdoidal breadth,
longer nasals, wider palate, and more inflated auditory bullae. The
posterior border of the hard palate is straight in five skulls of the
series that are complete (two skulls have the palatal regions broken);
all _C. g. limitis_ examined have a median posterior projection on
the posterior border of the hard palate.

_Measurements._--External and cranial measurements of the type, and
the average and extreme measurements of three adult males and two
adult females from the type locality (including the type) are: Total
length, 160, 145.6 (137-160); tail, 44, 40.8 (37-46); hind foot, 18.5,
19.3 (18-20); condylobasilar length, 23.3, 22.8 (22.1-23.5); zygomatic
breadth, 13.8, 13.4 (12.6-13.8); lambdoidal breadth, 11.5, 11.4
(11.0-11.6); alveolar length upper cheek-teeth, 5.5, 5.4 (5.2-5.5);
interorbital breadth, 3.8, 3.9 (3.8-4.0); length of nasals, 7.6, 7.1
(6.9-7.6); breadth of rostrum, 3.1, 3.1 (3.0-3.2); length of incisive
foramina, 5.5, 5.2 (5.0-5.5).

_Remarks._--Hall and Davis (Proc. Biol. Soc. Washington, 47:55,
February 9, 1934) reported 12 specimens of red-backed mice from
Hannagan Meadow, 9500 to 9600 ft., and ten from Hannagan Creek, 8600
ft., all in Greenlee County, Arizona. Although they pointed out most
of the cranial differences here described as diagnostic of _C. g.
arizonensis_, they did not name the animals as new since they had no
seasonally comparable materials; thus they were unable to evaluate the
differences noted in pelage. We have not examined the material
referred to by Hall and Davis (_loc. cit._), but, on the basis of
their description, here refer it to _C. g. arizonens