_Zygogeomys persimilis_ is represented by a rostral fragment bearing all the cheek teeth on the left side and the upper incisors. In addition, two lower jaws, one with the first three cheek teeth, are referred to the species (see Gazin, 1942:507). The fossils identified as _Geomys_ from the Arroyo San Francisco, Cedazo fauna, in Aguascalientes, México, by Mooser (1959:413) may be referable instead to _Zygogeomys_. I have not seen the specimens and no figures are available; Mooser states that a cranium was recovered. If either the upper premolar or third molar is in place, generic identification could be made with reasonable certainty. No other fossils of _Zygogeomys_ have been uncovered in late Pleistocene deposits and the significance of the absence of _Zygogeomys_ has been discussed in an earlier paragraph of this section. _Geomys_ has not been found so far south as Aguascalientes, but _Zygogeomys_ occurs farther south now and presumably had a more extensive range on the plateau to the north in the Pleistocene. _Geomys_ _Geomys_ is common in Pleistocene deposits, especially on the Great Plains. Certainly the center of differentiation for _Geomys_ was in this region, although at times, probably when conditions were favorable, _Geomys_ expanded its range into adjacent areas, reaching the Pacific Coast in Irvingtonian times and the Atlantic Coast at the time of the Illinoian glaciation. The earliest Pleistocene records of the genus are from the Great Plains. McGrew (1944:49) described _Geomys quinni_ from the Sand Draw local fauna, Brown County, Nebraska, considered by Hibbard (1958:11) to be Nebraskan in age. As mentioned in the account of Pliocene geomyids, _Geomys quinni_ occurs also in the late Pliocene deposits of southwestern Kansas. Also, _Geomys quinni_ occurs in the Broadwater-Lisco local fauna of Morrill and Garden counties, western Nebraska (Barbour and Schultz, 1937:3; Schultz and Stout, 1948:560-563; Schultz _et al._, 1951: table 1). The Broadwater-Lisco is currently regarded as Aftonian deposits (Schultz and Stout, _loc. cit._; Hibbard, 1958:11). Hibbard (1956:174) identified _Geomys quinni_ from the Deer Park local fauna, probably deposited during the early Aftonian interglacial, of Meade County, Kansas. Strain (1966:36) described _Geomys paenebursarius_ on the basis of fossils obtained from early Pleistocene deposits of the Hudspeth local fauna from western Hudspeth County in the Trans-Pecos of Texas. The Hudspeth fossils were probably deposited during the Aftonian interglacial. From Kingman County, Kansas, Hibbard (_op. cit._: 164) recovered isolated teeth of _Geomys_ from the Dixon local fauna, regarded by him (_op. cit._:153-154) as deposited during the latest Nebraskan glaciation, and correlated by him with the Sand Draw local fauna of Nebraska. Hibbard (1958:11) later regarded the Dixon as a transitional fauna between Nebraskan and Aftonian. The remains of _Geomys_ from the Dixon are known only from isolated teeth.