Of the molariform dentition only the lower premolar and first two lower molars are known. The enamel investment of p4 is complete, and would not be subject to interruption at any stage of wear; the two prisms are joined at their mid-points, and the isthmus of dentine is relatively broad (as in _Pliosaccomys_) when compared with modern pocket gophers of this tribe. Also, the re-entrant folds, rather than having parallel sides, diverge broadly to the sides. The divergence is especially noticeable in the labial fold. The lower deciduous premolar would have formed essentially the same enamel pattern with wear as observed in _Nerterogeomys_ [= _Zygogeomys_] cf. _minor_ (see Hibbard, 1954:fig. 5, A and B) and _Pliosaccomys dubius_ (see Wilson, 1936; pl. 1, fig. 1). Each molar is a single column in the final stages of wear; pre-final stages are unknown. Anterior and posterior enamel plates are present on m1 and m2 (m3 has not been recovered). The dentine tracts of m1 are exposed over a relatively wide surface; therefore, the enamel plates are distinctly separated. The tracts of dentine of m2 are much narrower than in m1 and the enamel plates are barely separated at the anterolateral margin of the tooth. Possibly the enamel band of m2 was continuous in an earlier stage of wear. The mandible is stout and its general construction not unlike that in modern geomyines. The capsule at the base of the angular process that receives the terminal end of the lower incisor is well developed. The base of the angular processes is preserved, and suggests that the process was short and decidedly smaller than in living examples of the tribe. The masseteric ridge is distinct but weakly developed, and not at all massive as in living pocket gophers. The mental foramen is immediately anterior, and slightly ventral, to the anterior extension of the crest. The basitemporal fossa is absent as such, but its position is marked by a slight depression. _Specimens examined._--Two rami; nos. 29147 (holotype) and 33446; several isolated teeth 30194 and 30195, including an upper incisor and a dp4 (deciduous lower premolar), all from Univ. Michigan Mus. Paleo. _Referred species._--One. *_Pliogeomys buisi_ Hibbard, 1954. Papers Michigan Acad. Sci., Arts, and Letters, 39:353. Type from Buis local fauna, latest middle Pliocene, Beaver County, Oklahoma. Genus =Zygogeomys= Merriam 1895. _Zygogeomys_ Merriam, N. Amer. Fauna, 8:195, January 31. 1942. _Nerterogeomys_ Gazin, Proc. U. S. Nat. Mus., 92:507 (type, _Geomys persimilis_ Hay, 1927). _Type._--_Zygogeomys trichopus_ Merriam, 1895, from Nahuatzen, Michoacán. _Chronologic range._--Late Pliocene (Benson and Curtis Ranch local faunas, Arizona, and ?Rexroad Formation, Kansas) to Recent.