_Distribution._--Desert lowlands of northeastern Coahuila, from the Río Grande to as far southwestward as the Río 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 convex in dorsal outline; zygomata widely flaring; palate short; rostrum short; nasals short; mastoid and tympanic bullae inflated; basioccipital with lateral edges parallel; maxillary teeth small. _Comparisons._--From _Cratogeomys castanops convexus_, found to the north, _bullatus_ differs in: Hind foot shorter; skull much broader in relation to length; rostrum narrower but, relative to length of skull, wider; tympanic bullae slightly more inflated; incisors and maxillary teeth smaller. From topotypes of _Cratogeomys castanops angusticeps_, found across the Río Grande and upstream from localities where _bullatus_ is known to occur, _bullatus_ differs in: Body slightly smaller; color paler, especially on sides; skull shorter and broader; rostrum shorter and broader; nasals shorter; mastoid and tympanic bullae more inflated; maxillary teeth smaller. For comparisons of _bullatus_ with the subspecies of _C. castanops_ found to the west and south, see accounts of the subspecies to follow. _Remarks._--_Cratogeomys castanops bullatus_ in small size resembles _C. c. tamaulipensis_ Nelson and Goldman of the lower Río Grande Valley in Tamaulipas, but the two differ markedly in cranial features. _Cratogeomys c. bullatus_ is smaller than _convexus_ but these two subspecies resemble each other in color and cranial characters. Both have an arched skull, inflated mastoid and tympanic bullae, short nasals, and a short rostrum. Comparison of _bullatus_ with _angusticeps_, which occurs across the Río Grande but not directly opposite the range of _bullatus_, indicates that these two subspecies are less closely related than _bullatus_ is to _tamaulipensis_ and _convexus_. _Cratogeomys castanops bullatus_ is especially common in sandy soils in the vicinity of Nava where the mounds were in fallow irrigated fields and other open places between extensive live oak thickets. South and west of the Río Grande the animals were less abundant and lived in heavier soils usually as individuals or in small groups. Specimens were taken at elevations from as low as 800 feet to as high as 2,000 feet. _Specimens examined._--Total, 24, from: 2 mi. S and 6-1/2 mi. E Nava, 810 ft., 2; 2 mi. S and 12 mi. E Nava, 800 ft., 1; _3 mi. S and 12 mi. E Nava, 800 ft._, 4; 29 mi. N and 6 mi. E Sabinas, 5; 10 mi. E Hacienda La Mariposa, 2000 ft., 1; La Gacha [= La Concha], 1600 ft., 8; 8 mi. S and 8 mi. E Hacienda La Mariposa, 1900 ft., 1; 9 mi. S and 11 mi. E Sabinas, 1050 ft., 2. +Cratogeomys castanops ustulatus+ new subspecies