Actual intergradation, in the sense of interbreeding between individuals of a continuously distributed population of animals, probably does not occur regularly between _S. f. cognatus_ and _S. f. robustus_ nor between several populations within either one of these subspecies; in south-central Arizona and western Texas the animals are said to occur only in the higher parts of the mountains. Consequently a given population is separated from another by low-lying territory inhospitable to the species _Sylvilagus floridanus_. This low-lying territory is inhabited by another species, _Sylvilagus audubonii_. More intensive collecting in the region concerned may, however, show a continuous distribution of the species _Sylvilagus floridanus_ in several areas where it seems now to have an interrupted distribution.
1907. _Sylvilagus audubonii neomexicanus_ Nelson, Proc. Biol. Soc. Washington, 20:83, July 22.
Nelson (N. Amer. Fauna, 29:230, August 31, 1909) listed under _Sylvilagus audubonii cedrophilus_ Nelson an adult female, skin with skull (U.S. Nat. Mus., Biol. Surv. Coll., No. 108698) from fifteen miles south of Alpine, Texas. Nelson (_loc. cit._) remarked that the "bleached" color of the back and the great lateral breadth of the tympanic bullae of No. 108698 were peculiarities not possessed by any other specimen examined. Geographically, the locality of capture is far south of other known occurrences of _S. a. cedrophilus_ and approximately on the boundary separating the range of _S. a. minor_ from that of _S. a. neomexicanus_. The large size, which may have induced Nelson to refer the specimen to _S. a. cedrophilus_, is not surprising considering that the individual is a female and fully adult. A combination of new and old fur on the upper parts presents a pattern that might be duplicated in other specimens of _S. a. neomexicanus_. The lateral inflation of the tympanic bullae can be interpreted as intergradation with the geographically adjacent _S. a. minor_ to the south; _S. a. minor_ has large bullae. There are no features otherwise which suggest that the specimen is anything other than _Sylvilagus audubonii neomexicanus_ and we refer it to that subspecies.
1896. _Lepus arizonae minor_ Mearns, Proc. U.S. Nat. Mus., 18:557, June 24.