(A. M. N. H.) American Museum of Natural History. (N. H. M. S. D.) Natural History Museum of San Diego. (M. V. Z.) Museum of Vertebrate Zoölogy, University of California. (U. M.) Museum of Zoölogy, University of Michigan. (C. M.) Carnegie Museum. (R. H.) Collection of Ross Hardy. (B. Y. U.) Brigham Young University. (U. S. N. M.) United States National Museum. (U. S. A. C.) Utah State Agricultural College. (K. U.) Museum of Natural History, University of Kansas.
[Illustration: FIG. 1. Map showing the distribution of species and subspecies of pocket gophers in Utah.]
1. _T. t. gracilis_ 2. _T. t. wasatchensis_ 3. _T. t. oquirrhensis_ 4. _T. t. uinta_ 5. _T. t. pygmaeus_ 6. _T. t. ravus_ 7. _T. t. ocius_ 8. _T. t. moorei_ 9. _T. t. fossor_ 10. _T. t. parowanensis_ 11. _T. t. levis_ 12. _T. b. aureiventris_ 13. _T. b. robustus_ 14. _T. b. minimus_ 15. _T. b. nesophilus_ 16. _T. b. stansburyi_ 17. _T. b. albicaudatus_ 18. _T. b. bonnevillei_ 19. _T. b. centralis_ 20. _T. b. sevieri_ 21. _T. b. convexus_ 22. _T. b. tivius_ 23. _T. b. contractus_ 24. _T. b. lenis_ 25. _T. b. levidensis_ 26. _T. b. osgoodi_ 27. _T. b. howelli_ 28. _T. b. wahwahensis_ 29. _T. b. dissimilis_ 30. _T. b. aureus_ 31. _T. b. birdseyei_ 32. _T. b. virgineus_ 33. _T. b. planirostris_ 34. _T. b. absonus_ 35. _T. b. alexandrae_
All pocket gophers of Utah belong to the genus _Thomomys_. There are only two species within the state, _Thomomys bottae_ with twenty-four subspecies and _Thomomys talpoides_ with eleven subspecies.
Due to marked mutational capacities and ready response to environmental pressures and sedentary habits, pocket gophers differentiate readily into numerous subspecies. It is well known that Utah by its highly varied topography and climate possesses widely different types of habitats. The aforementioned plasticity of these animals and possibly the fact that both species are at the extreme limits of their ranges in Utah account for the numerous forms found within the state.
The genus may be characterized as follows: Highly specialized fossorial rodents, with heavy, thick bodies; all four legs of approximately equal length, but front legs more muscular for digging, and feet provided with long claws; external fur-lined cheek pouches; small eyes, short ears and tail; upper incisors long and projecting external to lips. Skull: Stout and flattened; zygomatic arches well developed and usually widely spreading; all teeth with permanent pulp cavities; incisors superficially smooth, but fine median groove present on anterior face of each upper incisor; dental formula, i. 1/1, c. 0/0, p. 1/1, m. 3/3; external auditory canal long; stapedial artery small and enclosed within an osseous canal.