All three lower molars are single, compressed, elliptical columns with enamel on only the posterior surfaces. M1 and M2 are also elliptical in cross-section and decidedly anteroposteriorly compressed, like the lower molars. Nevertheless, the enamel pattern is variable; enamel plates may be retained completely across both the anterior and posterior walls of M1 and M2 or only the anterior plate may be retained without reduction and the posterior plate may be reduced so that only a vestige is retained on the lingual fourth of the tooth or the posterior plate may be completely lost. M3 tends to remain at least incompletely bilophodont by reason of retaining a permanent labial re-entrant fold in most species (with exceptions in _Pappogeomys bulleri_ and some old adults of _P. castanops_). Primitively the occlusal surface of M3 is subtriangular (subgenus _Pappogeomys_), but in the _castanops_ species-group of the advanced subgenus _Cratogeomys_, the posterior loph usually is reduced and the occlusal surface is quadriform or obcordate. Curiously, the trend towards reduction of the posterior loph is reversed in one subspecies (_P. merriami fulvescens_) and, the loph has elongated into a pronounced heel in some specimens, resembling the condition in _Orthogeomys_. The entire range of variation occurs in _P. m. fulvescens_. The subtriangular pattern is retained in the most specialized species of _Cratogeomys_ where that pattern is associated with extreme platycephaly in the _gymnurus_ species-group. In most species the posterior loph supports two lateral plates, the outer one always bordering the labial re-entrant fold. In _Pappogeomys bulleri_ and in the _castanops_ species-group, the outer re-entrant fold of M3 tends to be obsolete, and the tooth becomes quadriform or suborbiculate in some individuals and loses the bilophodont pattern that characterizes other species. The lingual enamel plate is displaced to the posterior surface of the tooth, and one or both plates may disappear with advancing age. Consequently, only the anterior enamel plate remains in some adults, and constitutes the maximum degree of reduction of enamel on M3 in the Geomyinae. In many adults of _Pappogeomys bulleri_, the enamel investment of the posterior loph is complete and the two lateral plates are connected, without interruption around the posterior apex of the tooth, evidently representing the retention of a primitive character of the ancestral lineage. The m3 of _P. bensoni_ from the late Pliocene is distinguished by minute lateral inflections suggesting the primitive biprismatic pattern. Also the posterior enamel plates of m1 and m2 are remarkably long, extending around the ends of the tooth. The associated upper incisor was unisulcate as in the modern species, and the basitemporal fossa of the mandible is well developed and deep.