skull narrower;
zygomata more nearly parallel and less expanded anteriorly; rostrum
narrower and longer; nasals longer; squamosal breadth greater; mastoid
bullae less inflated; maxillary teeth smaller. From _Cratogeomys
castanops bullatus_, found to the east, _sordidulus_ differs in: Body
larger; hind foot larger; upper parts darker, more ochraceous and less
buffy; skull larger in all respects; zygomata more widely flaring;
tympanic bullae less inflated; maxillary teeth larger.

_Remarks._--_Cratogeomys castanops sordidulus_ is limited to the
Llano de Ocampo, an elevated, desert plain surrounded on three sides,
west, south and east, by higher mountainous country which seems to bar
the passage of this rodent. On the eastern side this barrier extends
north to the very banks of the Rio Grande in the Canon de Boquillas.
This subspecies, therefore, is in contact with other populations of
_Cratogeomys_ only to the north and northwest. This subspecies is well
characterized by size, color and cranial characteristics.

_Cratogeomys castanops sordidulus_ is not abundant; groups of mounds
constructed by one or a few individuals were found in widely separated
places. Mounds were often small, appeared old and, in other ways, were
inconspicuous on arid flats. The animals were taken at elevations as
low as 3250 feet and as high as 4150 feet.

_Specimens examined._--Total, 13, from: 50 mi. N and 20 mi. W Ocampo,
4150 ft., 1; 18 mi. S and 14 mi. E Tanque Alvarez, 4000 ft., 4; 1-1/2
mi. NW Ocampo, 3300 ft., 6; _Ocampo_, 1; 5 mi. N and 19 mi. W Cuatro
Cienegas, 3250 ft., 1.

+Cratogeomys castanops consitus+ Nelson and Goldman

1934. _Cratogeomys castanops consitus_ Nelson and Goldman, Proc. Biol.
Soc. Washington, 47:140, June 13, type from Gallego, 5500 ft.,
Chihuahua.

_Distribution._--Arid high plains from central Chihuahua, east and
southeast at least into northwestern Coahuila (see fig. 1).

_Comparisons._--From _Cratogeomys castanops lacrimalis_ Nelson and
Goldman, specimens from Boquillas and Marathon north of the Rio Grande
in Texas, _consitus_ differs in: Body smaller; tail and hind foot
shorter; upper parts paler, more light buffy and less rufous;
underparts paler, light buffy instead of dark buffy; skull decidedly
smaller; zygomata slightly less widely flaring; palate especially
shorter; rostrum narrower; squamosal breadth less; incisors smaller.
From topotypes of _Cratogeomys castanops clarkii_, found to the north