_Remarks._--The geographic range of _convexus_ is restricted, being bounded on the west and southwest by mountains, especially the Serranías del Burro, and on the north and east by the Río 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 Acuña and Piedras Negras, along the Río 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 Río 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 Río Grande is an effective barrier to passage by these rodents.
_Specimens examined._--Total, 14, all from Coahuila: Río Grande, 17 mi. S Dryden, Terrell Co., Texas, 6; Río Grande, opposite Samuels, Val Verde Co., Texas, 1 (BSC); Villa Acuña, 5; Cañon 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 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.