elson and Goldman (Proc. Biol. Soc.
Washington, 47:135-154, June 13, 1934) revised the genus _Cratogeomys_
and decided that six subspecies of _C. castanops_ occurred in
Coahuila. In the present account, we describe four previously unknown
subspecies from Coahuila, exclude from the state two others recorded
from there by Nelson and Goldman, and show that three others named
previously from adjacent Mexican states do occur in Coahuila. This
makes eleven subspecies now known from that state. From Coahuila
Nelson and Goldman had 35 study specimens of _C. castanops_ from seven
localities and we have had 234 specimens from 63 localities.
Consequently we have been able to define with greater certainty, than
formerly was possible, the geographic distribution of _C. castanops_
in this Mexican state and similarly analyze more completely the
geographic variation.

Coahuila is near the center of the geographic range of _C. castanops_.
The occurrence of 11 subspecies within the state seems to be
the result of partial or perhaps, in some cases, total isolation of
populations of _C. castanops_ because of the highly dissected
topography and the variability of the soil. _Cratogeomys castanops_ is
a sedentary animal preferring open plains mantled by suitable soils,
preferably sandy in texture, in which the animals can dig their
elaborate underground systems of runways. Thin soils of hard texture
and rocky soils do not offer optimum habitat for _C. castanops_, and
the animals usually are absent or uncommon in such situations. Desert
mountains with their thin rocky soils, elevated passes, perpendicular
rocky cliffs, and stands of oaks and conifers at higher elevations
present impassable barriers for pocket gophers of this species. The
Rio Grande, bordering Coahuila to the north, in many places flowing
through steep-walled canons, also seems to be a barrier that this
fossorial rodent does not cross; distinct subspecies occur on the two
sides of the river directly opposite each other (also see Nelson and
Goldman, _op. cit._: 143). Smaller streams, such as the Rio Salado,
Rio Nazas and Rio Salinas, seem to be unimportant barriers to the
passage of these pocket gophers. The food supply of _C. castanops_
seems adequate in most situations and consequently food is unimportant
in governing the distribution of this species. Principal foods of _C.
castanops_ are fleshy tuberous roots of well-distributed desert
shrubs, but in the valleys of the high