_Pliogeomys buisi_ Hibbard (1954:353) was found in the Buis Ranch local fauna, of latest middle Pliocene, on the west side of Buckshot Arroyo, Beaver County, Oklahoma. The original material included a right ramus bearing the premolar and first two molars (the holotype) and five isolated premolars and molars. One of the molars is slightly worn and from an immature individual. One premolar is a deciduous tooth. Hibbard (_op. cit._:342) identified the beds from which he obtained the Buis Ranch local fauna as from the lowermost part of the Upper Pliocene. Moreover, he judged the Buis Ranch local fauna to be only slightly older than the Saw Rock Canyon local fauna of Seward County in southwestern Kansas. Previously (Hibbard, 1953:408-410), the Saw Rock Canyon local fauna had been assessed as older than the Rexroad local faunas (latest late Pliocene) and, therefore, representative of the early part of the late Pliocene. More recently, Hibbard (1956:164) identified the Buis Ranch beds as part of the Ogallala Formation, which here occurs unconformably just beneath the Rexroad Formation (composed of strata nearly all of late Pliocene age). Therefore, he regarded the Buis Ranch beds as latest middle Pliocene in age. Hibbard (1954:356) suggested that pocket gopher remains from the Saw Rock Canyon local fauna were referable to _Pliogeomys buisi_, and, in effect, tentatively assigned them to _Pliogeomys_ (in his description of the genus Hibbard remarked that the upper incisor is bisulcate as in _Geomys_, and the only upper incisor that he mentions was one of the Saw Rock Canyon fossils and not part of the Buis Ranch material). _Pliogeomys_ has closer affinities with modern pocket gophers of the tribe Geomyini than it does with the middle Pliocene genus _Pliosaccomys_. The pocket gopher fauna known from the late Pliocene was more varied than the faunas known from any earlier time. In addition to the extinct _Pliogeomys_, which occurs in early late Pliocene (see discussion above), the living genera _Zygogeomys_, _Geomys_, _Pappogeomys_ (in the sense used on p. 534), and _Thomomys_ first appear in the late Pliocene. The only other living genus, _Orthogeomys_, makes its first appearance in the late Pleistocene. The earliest record of the genus _Thomomys_ is based on a fragment of a left mandibular ramus bearing p4 and m1, _Thomomys gidleyi_ Wilson (1933b:122), from the Hagerman local fauna of Twin Falls County, Idaho. Wilson (_loc. cit._) was uncertain as to age (late Pliocene or early Pleistocene) but subsequently (1937:38 and 67-70) settled on the middle part of the late Pliocene. Hibbard (1958:11) later considered the age as early Pleistocene (suggesting that the deposits accumulated in the Aftonian interglacial interval) but subsequently (Hibbard _et al._, 1965:512), on the basis of potassium argon age determinations, also settled on late Pliocene.