Fig. 1. Geographic ranges of the subspecies of Cratogeomys castanops
found in Coahuila, México.
| Guide to subspecies | 4. | C. c. bullatus | 8. | C. c. subsimus | |
| 1. | C. c. convexus | 5. | C. c. ustulatus | 9. | C. c. goldmani |
| 2. | C. c. consitus | 6. | C. c. jucundus | 10. | C. c. subnubilus |
| 3. | 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 Río 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 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.