The lower jaw is stout and relatively short. The masseteric ridge is well developed and has an especially thick crest. The basitemporal fossa is deep. In most living species, the pelage is soft and dense, but in one species, _Pappogeomys fumosus_, the hairs are coarse and hispid somewhat as in _Orthogeomys_. Key to the Subgenera of _Pappogeomys_ A Enamel plates completely developed across posterior walls of M1 and M2, except in one species (_P. alcorni_) having enamel restricted to lingual fourth in M1; sagittal crest lacking owing to impressions of temporal muscles remaining separated (even in old adults); zygomata slender, and without platelike expansion at lateral angle. Subgenus _Pappogeomys_ p. 534 A´ Enamel lacking on posterior walls of M1 and M2; pronounced sagittal crest developed in adults of both sexes by union of temporal impressions at middorsal line; zygomata stout and wide, with lateral angle expanded into broad plate. Subgenus _Cratogeomys_ p. 535 Subgenus =Pappogeomys= Merriam 1895. _Pappogeomys_ Merriam, N. Amer. Fauna, 8:145, January 31. _Type._--_Geomys bulleri_ Thomas, 1892, from near Talpa, west slope Sierra de Mascota, 8500 ft. (actually about 5000 ft.), Jalisco. _Chronologic range._--Late Pliocene (Benson local fauna, Arizona) to Recent, but no specimens known from Pleistocene. _Description._--Small, approximately same size as small subspecies of _Thomomys umbrinus_ but forefeet larger and claws longer; skull of generalized shape, broad, relatively short, smoothly rounded, not especially compressed dorso-ventrally; zygomatic breadth great but not exceeding mastoid breadth; zygomata relatively slender for geomyid and lacking platelike expansions at lateral angles; rostrum relatively narrow; sagittal crest lacking, owing to impressions of temporal muscles remaining separated; angular process of mandible not especially elongated; enamel plates extending completely across posterior wall of M1 and M2, except in one species, _P. alcorni_, where posterior plate of M1 remains only on lingual fourth of posterior wall (remainder of plate lacking); with wear, plates sometimes exceptionally thin completely across posterior face of M2 and especially M1 in a few individuals of _P. bulleri_ much as Paulson (1961:138-139) describes in extinct _Geomys tobinensis_; one or both plates rarely disappear in final stages of attrition in old individuals resulting in same dental pattern found in _Cratogeomys_; M1 and M2 retaining enamel plate on anterior wall throughout life; M3 usually subtriangular in cross-section but sometimes suborbiculate or ovoid, crown slightly bilophodont owing to shallowness of labial re-entrant angle in modern species; posterior loph of M3 not especially elongated and crown not significantly longer than wide; both lateral enamel plates of M3 usually well developed and