palate, rostrum and nasals; mastoid and tympanic bullae less inflated; squamosal breadth greater. _Remarks._--_Cratogeomys castanops jucundus_ is large, exceeding subsimus in dimensions of the body, but differing from _subsimus_ in relatively smaller skull. Passage to the north and northeast by _jucundus_ is at least partly blocked by inhospitable mountainous country; the resulting semi-isolation may be one reason for the distinctive characteristics of _jucundus_ compared with those of _bullatus_ and _ustulatus_. Two specimens from Monclova, assigned to _tamaulipensis_ by Nelson and Goldman (op. cit.:142), are here referred to _jucundus_ on the basis of cranial characters and size. Specimens were trapped in fallow irrigated fields in the vicinity of Monclova. Others were taken in deep soils in desert flats. _Specimens examined._--Total, 19, from: Hermanas, 1205 ft., 9; _1 mi. S Hermanas_, 2; 1 mi. N and 13 mi. E Cuatro Ciénegas, 2; 5 mi. N and 2 mi. W Monclova, 1; _2 mi. N and 1 mi. E Monclova_, 1; Monclova, 2 (BSC); Hisachalo [= Huisachalo], 2. +Cratogeomys castanops sordidulus+ new subspecies _Type._--Female, adult, skin and skull; No. 56614, Univ. Kansas Mus. Nat. Hist.; 1.5 mi. NW Ocampo, 3300 ft., Coahuila; 16 December 1953; obtained by Robert W. Dickerman, original number 2164. _Distribution._--Desert plains of north-central Coahuila, surrounded for the most part by higher mountainous country (see fig. 1). _Diagnosis._--Body large for species (see tables 1 and 2); tail short; hind foot large; upper parts Ochraceous-Buff (in summer pelage) and Orange-Buff (in fresh winter pelage); underparts Pale Ochraceous-Salmon; skull medium in size and narrow; zygomata narrow; rostrum narrow; palate short; nasals medium in length; basioccipital small and narrow; mastoid bullae not greatly inflated; tympanic bullae inflated; incisors small; maxillary teeth small.