species and stated that there is no evidence of intergradation with
other named kinds. We have examined the holotype and three topotypes
(202579-202582 BS) and compared them with specimens of other kinds of
pocket gophers occurring in northern and central Arizona. The _muralis_
gopher is a depauperate form clearly belonging to the _bottae_ group.
The characters which Goldman (_loc. cit._) set forth as distinguishing
_muralis_ from other named kinds are readily apparent and, like Goldman,
we see no evidence of intergradation. Nevertheless, the characters which
serve to identify the race are, in a general way, those commonly found
in populations of depauperate individuals of _Thomomys bottae_ and _T.
talpoides_. The small size, delicate structure, well-inflated braincase,
short premaxillary tongues, and strongly recurved upper incisors, often
appear in populations existing in inhospitable areas of shallow,
unstable soils. For this reason we feel that the relationships of this
population are best shown by arranging _muralis_ as a subspecies of
_Thomomys bottae_; the name should stand as _Thomomys bottae muralis_
Goldman.

As far as known, _T. b. muralis_ is completely isolated from other
populations of pocket gophers by uninhabitable eroding cliffs. The
animals have been found only on isolated terraces in the lower end of
Prospect Valley (itself a lateral pocket) within the Grand Canyon of the
Colorado River, Hualpai Indian Reservation, Arizona. Consequently it is
unlikely that intergradation with other populations could exist at the
present time.

In short, in arranging _muralis_ as a subspecies of _Thomomys bottae_,
we are influenced, not by the demonstration of intergradation, but by
the degree of morphological differentiation of the population and the
probable reasons therefor.

~Thomomys bottae mutabilis~ Goldman

Goldman (Jour. Washington Acad. Sci., 28:342, July 15, 1938) named the
subspecies _Thomomys bottae pinalensis_ on the basis of only one
specimen, an immature female (245709 BS) from Oak Flat, five miles east
of Superior, Pinal Mountains, Arizona. Examination shows it to be
indistinguishable in characters of taxonomic importance (coloration,
external measurements, shape of skull and size of skull) from specimens
of _T. b. mutabilis_ of comparable sex and age. No. 245709 is well
within the limits of individual variation of _T. b. mutabilis_ as is
shown by the several specimens (all in the U. S. Biologic