Three extinct species of _Thomomys_, all referable to the subgenus _Thomomys_, have been described. _Thomomys microdon_ Sinclair (1905:146), based on the rostral portion of a skull without a mandible, is from the Potter Creek Cave local fauna, Shasta County, California, and has been recovered also from Samwel Cave, Shasta County, California. _T. microdon_ closely resembles _Thomomys monticola_ that lives in the area today. _Thomomys scudderi_ Hay (1921:614) is from the Fossil Lake (or Christmas Lake) local fauna in central Oregon. Elftman (1931:10-11) referred these specimens to _Thomomys townsendii_, and he considered _T. scudderi_ to be a synonym of _T. townsendii_. Davis (1937:156-158) disagreed with Elftman concerning the taxonomic status of _T. scudderi_, which he regarded as a valid species. According to Davis, _T. scudderi_ is more closely allied to _Thomomys bottae_ than to _T. townsendii_. Cope (1878:389; 1889:160-165) had referred the same specimens to _Thomomys clusius_ (now _Thomomys talpoides clusius_). Cope considered the beds to be Pliocene in age. In all accounts of the Fossil Lake local fauna up to Hay (1921), the specimens of _Thomomys_ were referred to the species _clusius_, _talpoides_, or _bulbivorus_ (see Elftman, _loc. cit._). The Fossil Lake local fauna is currently considered as being of Rancholabrean provincial age, probably dating from the Wisconsin glacial maximum when the lake reached its greatest size. The third extinct species described from the Wisconsin is _Thomomys vetus_ Davis (1937:156), also from the Fossil Lake local fauna in Lake County, Oregon. Davis pointed out that _T. vetus_ differs from _T. scudderi_ Hay, of the same fauna, in larger size and other cranial details, and that it is closely allied to the living species _Thomomys townsendii_, and not to _Thomomys talpoides_, which is the only species of _Thomomys_ living in the area today. _Thomomys townsendii_ was recovered by Gazin (1935:299) from the American Falls beds (probably Wisconsin deposits) in Idaho. _Thomomys talpoides_ is reported from the Howard Ranch local fauna in Hardeman County, western Texas, by Dalquest (1965:69-70), who referred the isolated teeth to _T. talpoides_ on geographic grounds, apparently on the erroneous assumption that _T. talpoides_ was the species of _Thomomys_ nearest geographically to Hardeman County. Hay (1927:259) reported _Thomomys fuscus_ [= _Thomomys talpoides_] from late Pleistocene beds near Wenatchee, Chelan County, Washington. Hibbard (1951:229) recorded _Thomomys talpoides_ from late Pleistocene deposits in Greeley County, Kansas, and Walters (1957:540) reported the same species from late Pleistocene deposits in Clark County, Kansas. According to Hibbard (1958:14) other remains reported as _T. talpoides_ have been recovered from numerous areas of Wisconsin glacial drift in western North America.