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.
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.
Description and discussion.—The size is small to medium for the subfamily Geomyinae. This genus is distinguished principally by the retention of primitive features. In the living species, the skull is generalized, rather than specialized toward either extreme dolichocephaly or platycephaly. The angular process is short, barely exceeding the lateral extensions of the mastoid process of the squamosal. The rostrum is remarkably narrow in relation to its length. The jugal is reduced and displaced ventrally, causing the maxillary arm of the zygomata to articulate with the squamosal arm of the zygomata along the dorsal border of the zygomatic arch (a feature observed also in Orthogeomys cherriei costaricensis).