_Specimens examined._--Total, 10, from: Don Martin, 800 ft., 5; _base of Don Martin Dam_, 2; _2 mi. SE Don Martin Dam, along Río Salado_, 2; 5 mi. SE Don Martin, 1. _Records from Nuevo León._--Total, 14, from: 9 mi. N and 2 mi. W Anahuac [= Rodríques], 1; 4 mi. N and 1 mi. W Anahuac [= Rodríques], 5; 3 mi. N Lampazos, 4; 1 mi. N Vallecillo, 1000 ft., 1; Vallecillo, 20 mi. S Río Salado, 1000 ft., 3. +Cratogeomys castanops jucundus+ new subspecies _Type._--Female, adult, skin and skull; No. 56603, Univ. Kansas Mus. Nat. Hist.; Hermanas, 1205 ft., Coahuila; 5 December 1953; obtained by Robert W. Dickerman, original number 2051. _Distribution._--Arid plains and broad intermontane valleys of east-central Coahuila (see fig. 1). _Diagnosis._--Body largest for the species (see table 1); tail long; hind foot large; upper parts in winter pelage Ochraceous-Buff, in summer pelage Antimony Yellow; underparts Pale Ochraceous-Buff; skull medium in size, broad; zygomata moderately flaring; palate medium in length; rostrum broad; nasals moderately long; maxillary teeth small. _Comparisons._--From _Cratogeomy castanops ustulatus_, found to the east, jucundus differs in: Body larger; tail longer; hind foot larger; upper parts paler, more ochraceous and less rufous; skull averaging smaller; zygomata slightly less expanded laterally; palate and nasals shorter; squamosal breadth less; mastoid bullae less inflated, especially in females; rostrum slightly narrower; maxillary tooth-row shorter. From topotypes of _Cratogeomys castanops tamaulipensis_, found to the southeast, _jucundus_ differs in: Body larger; tail longer; hind foot smaller; upper parts, in winter pelage, paler, more ochraceous and less rufous; skull larger; zygomata more widely flaring; palate longer; rostrum broader; tympanic bullae more inflated; basioccipital with sides parallel instead of convex; maxillary teeth smaller. From _Cratogeomy castanops excelsus_, found to the southwest, _jucundus_ differs in: Body larger; hind foot averaging larger; upper parts darker, more ochraceous, and less buffy; underparts darker, more buffy and less whitish; skull slightly smaller; zygomata less widely flaring, especially in females; palate shorter; nasals shorter; squamosal breadth less; mastoid bullae more inflated; incisors narrower. From _Cratogeomys castanops subsimus_, found to the south, _jucundus_ differs in: Body larger; tail shorter; hind foot shorter; upper parts paler, more ochraceous and less yellowish; skull smaller; zygomata less widely expanded laterally; palate and nasals shorter; rostrum narrower; squamosal breadth less; maxillary tooth-row shorter. From _Cratogeomys castanops bullatus_, found to the north, _jucundus_ differs in: Body larger; tail averaging longer; hind foot larger; color of upper parts more ochraceous and less rufous; underparts darker, more buffy and less whitish; skull larger, especially in length, in width across zygomata, in lengths of