In the western part of the Great Plains this species is confined to the riparian growth along streams and _Sylvilagus audubonii_ occupies the remainder of the terrain. In New Mexico and southwestern Texas _S. floridanus_ is confined to the boreal life-zones where timber provides denser cover than is found in the lower life-zones. The zonal range is from the Canadian Life-zone into the Tropical Life-zone. It is not surprising, therefore, that there is much geographic variation in the shape and size of the skull. There is so much geographic variation in the skull that it is impossible, at this writing at least, to frame a description that will enable the reader to distinguish the skull from those of all other species of the genus. In any given area, however, it is possible, easily and certainly, to distinguish the skulls of _S. floridanus_ from those of the other species which occur in that area. SYLVILAGUS FLORIDANUS ALACER (Bangs). 1896. _Lepus sylvaticus alacer_ Bangs, Proc. Biol. Soc. Washington, 10:136, December 28, type from Stilwell, Boston Mountains, Adair County, Oklahoma. _Marginal records._--Missouri (Nelson, 1909:176): Columbia; St. Louis. Illinois: Ozark (Necker and Hatfield, 1941:56). Tennessee (Nelson, 1909:176): Samburg; Raleigh. Mississippi (Nelson, 1909:176): Michigan City; Bay St. Louis. Texas (Nelson, 1909:176): Port Lavaca; Brazos; Henrietta. Oklahoma: Norman (Blair, 1939:128). Kansas: _8 mi. NE Harper_ (12917 KU); Rago (12508 KU); Halstead (3110 KU); _4 mi. S_ and _14 mi. W Hamilton_ (13673 KU); 3 mi. N Chanute (22026 KU). SYLVILAGUS FLORIDANUS AMMOPHILUS A. H. Howell. 1939. _Sylvilagus floridanus ammophilus_ A. H. Howell, Jour. Mamm., 20:365, August 14, type from "Oak Lodge", on peninsula opposite Micco, Florida. Known from type locality only. [Illustration: FIG. 39. Distribution of _Sylvilagus nuttallii_, _S. floridanus_ and _S. insonus_. Guide to kinds: 1. _S. n. nuttallii_ 2. _S. n. grangeri_ 3. _S. n. pinetis_ 4. _S. f. similis_ 5. _S. f. mearnsi_ 6. _S. f. llanensis_ 7. _S. f. alacer_ 8. _S. f. mallurus_ 9. _S. f. hitchensi_ 10. _S. f. floridanus_ 11. _S. f. ammophilus_ 12. _S. f. cognatus_ 13. _S. f. robustus_ 14. _S. f. chapmani_ 15. _S. f. holzneri_ 16. _S. f. restrictus_ 17. _S. f. subcinctus_ 18. _S. f. orizabae_ 19. _S. f. connectens_ 20. _S. f. russatus_ 21. _S. f. aztecus_ 22. _S. f. chiapensis_ 23. _S. f. yucatanicus_ 24. _S. f. hondurensis_ 25. _S. f. costaricensis_ 26. _S. insonus_ ] SYLVILAGUS FLORIDANUS AZTECUS (J. A. Allen). 1890. _Lepus sylvaticus aztecus_ J. A. Allen, Bull. Amer. Mus. Nat. Hist., 3:188, December 10, type from Tehuantepec City, Oaxaca. 1904. _Sylvilagus_ (_Sylvilagus_) _floridanus aztecus_, Lyon, Smiths. Misc. Coll., 45:336, June 15.