C. c. sordidulus_ 7. _C. c. excelsus_ 11. _C. c. planifrons_]

_Comparisons._--From topotypes of _Cratogeomys castanops angusticeps_
Nelson and Goldman, found to the north and east across the Rio Grande
in Texas, _convexus_ differs in: Body larger; upper parts more
reddish, especially on sides; skull with zygomata less heavy, nasals
broader, pterygoids smaller, maxillary teeth larger. For comparisons
of _convexus_ with the subspecies of _C. castanops_ found to the west,
south and southeast, see accounts of the subspecies to follow.

_Remarks._--The geographic range of _convexus_ is restricted, being
bounded on the west and southwest by mountains, especially the
Serranias del Burro, and on the north and east by the Rio Grande. The
range of the subspecies found to the southeast may not be continuous
with that of _convexus_. At least, in the area between Villa Acuna and
Piedras Negras, along the Rio Grande, no specimens were obtained and
no sign was observed. We suspect that in this area the species occurs
only locally if at all.

A specimen taken near the Rio Grande in Coahuila, opposite Samuels,
Texas, and assigned to _Cratogeomys castanops clarkii_ by Nelson and
Goldman (op. cit.:140), has been examined by us and is referable to
_convexus_. This specimen is typical of _convexus_ except for the
lesser inflation of the mastoid bullae and tympanic bullae.
Conspicuous differences between _convexus_ and _angusticeps_
indicate that the Rio Grande is an effective barrier to passage by
these rodents.

_Specimens examined._--Total, 14, all from Coahuila: Rio Grande, 17
mi. S Dryden, Terrell Co., Texas, 6; Rio Grande, opposite Samuels, Val
Verde Co., Texas, 1 (BSC); Villa Acuna, 5; Canon del Cochino, 21 mi. E
and 16 mi. N Piedra Blanca, 1; 11 mi. W Hda. San Miguel, 1.

+Cratogeomys castanops bullatus+ new subspecies

_Type._--Female, adult, skin and skull, No. 48498, Univ. Kansas Mus.
Nat. Hist., 2 mi. S and 6-1/2 mi. E Nava, 810 ft., Coahuila; 16 June
1952; obtained by Robert J. Russell, original number 276.

_Distribution._--Desert lowlands of northeastern Coahuila, from the
Rio Grande to as far southwestward as the Rio Sabinas (see fig. 1).

_Diagnosis._--Body medium for the species (see tables 1 and 2); tail
long; hind foot small; upper parts Light Ochraceous-Buff (in summer
pelage) and Orange-Buff (in winter pelage), bases of hairs Plumbeous;
underparts white to pale buffy; skull small, broad and slightly