1. Upper incisors lacking conspicuous longitudinal grooves: Thomomys, 2
1'. Upper incisors with one or more conspicuous longitudinal grooves: 4
2. Found in the higher parts of the Animas Mountains, Hidalgo County: Thomomys umbrinus.
2'. Not found in the higher Animas: 3
3. Color yellowish, brownish, or blackish; anterior openings of infra-orbital canals not posterior to anterior palatine foramina: Thomomys bottae.
3'. Color grayish or brownish; anterior openings of infraorbital canals posterior to anterior palatine foramina: Thomomys talpoides.
4. Upper incisors each with one longitudinal groove: Cratogeomys castanops.
4'. Upper incisors each with two longitudinal grooves: Geomys bursarius.
Key after Findley (1987).
Last Update: 20 Jul 2005