1904. Sylvilagus floridanus holzneri, Lyon, Smithsonian Miscl. Coll., 45:336, June 15.
Examination of cottontail rabbits from Arizona in the Biological Surveys Collection and the United States National Museum indicates that Sylvilagus audubonii can be distinguished from Sylvilagus nuttallii and Sylvilagus floridanus by the larger (more inflated) tympanic bullae. Topotypes of Sylvilagus nuttallii pinetis and other specimens from Alpine, Mt. Thomas, Springerville, the Prieto Plateau at 9000 feet on the south end of the Blue Range, and the Tunitcha Mountains are characterized by a posteriorly pointed supraoccipital shield and a long, wide space between the braincase and the posterior extension of the supraorbital process. The cottontails with equally small tympanic bullae from more western and more southern localities are referable to Sylvilagus floridanus holzneri on the basis of a posteriorly truncate or emarginate supraoccipital shield and a narrower and shorter space (usually a "foramen") between the braincase and the posterior extension of the supraorbital process. In S. f. holzneri the posterior end of the posterior process fuses with the braincase whereas the posterior end of this process in Arizonan specimens of S. n. pinetis merely lies against the braincase or projects free of it. In specimens from Arizona the difference in shape of the posterior border of the supraoccipital shield and the difference in size of the space between the braincase and the posterior extension of the supraorbital process are the only differences of taxonomic worth found by us. Many other features of the skull, of color of pelage, and of size of external parts all fell within the range of individual variation of a series of specimens from one locality.
Specimens from the following localities in Arizona are referable to Sylvilagus floridanus holzneri (Mearns).
Hualpai Mts., Nos. 117461, 117462, 117488, 117490, 117495, 227735, and 227832; Ft. Whipple, No. 214157; Prescott, No. 34667/46752; Mayer, No. 247495; Reynolds Creek Ranger Station, Sierra Ancha Mts., Gila Co., No. 247734; Fish Creek, Tonto National Forest, 2000 ft., No. 212833; north base Mt. Turnbull, 4500 ft., No. 214339; Ash Creek, 6100 ft., Graham Mts., No. 204363; Pinery Canyon, 7500 ft., Chiricahua Mts., No. 247953; Thomas Cañon, 2 mi. E Baboquivari Mts., No. 244420; Pine Springs, 15 mi. south of Colorado Cañon, No. 2425 Amer. Mus. Nat. Hist. On December 4, 1950, we removed the skull of No. 2425 to more certainly ascertain the identity of the individual.
The specimens listed above include those that Nelson (N. Amer. Fauna, 29:211, August 31, 1909) listed from the Hualpai Mountains, Pine Springs, and Prescott under the name Sylvilagus nuttallii pinetis. Nelson (op. cit.:Pl. X, fig. 2) figured one of these skulls from the Hualpai Mountains as S. n. pinetis and the cranial measurements (op. cit.:201) that he records for S. nuttallii pinetis likewise are of these same specimens of Sylvilagus floridanus holzneri. Nelson's description (op. cit.:207–210) seems to have been affected by the erroneous (as we see the matter) inclusion of these specimens of S. f. holzneri in the materials identified by him as Sylvilagus nuttallii pinetis.
The specimens so far mentioned from Arizona can be identified with ease. The identification becomes difficult, however, when the holotype of S. f. holzneri, from the Huachuca Mountains, is examined. The difficulty results from the holotype having a barely detectable emargination in the posterior border of the supraoccipital shield. In this respect the holotype is intermediate between S. f. holzneri (as known by specimens from more western localities in Arizona) and S. n. pinetis from the White Mountains to the northward. As noted above, S. f. holzneri has a deep notch and S. n. pinetis has none. This intermediacy of the holotype supports the possibility, mentioned by Nelson (op. cit.:200), that intergradation occurs between S. f. holzneri and S. n. pinetis. Additional evidence, however, is against this possibility; the notch in the supraoccipital is deeper in specimens (No. 66136, from Chiricahua Mts., and No. 204364, from Ash Creek in Graham Mts.) from mountains geographically intermediate between the Huachuca Mountains and the White Mountains. Also, the holotype of S. f. holzneri differs from S. n. pinetis and agrees with other specimens of S. f. holzneri from farther southwest in Arizona in the robustness of the posterior extensions of the supraorbital processes and in the considerable degree of fusion of the tips of these processes with the squamosals. Additionally, the rostrum of the holotype is wide and deep as in other specimens of S. floridanus from more eastern localities and is unlike the narrow and shallow rostrum of S. n. pinetis.
If intergradation occurs in Arizona between the species Sylvilagus floridanus and Sylvilagus nuttallii, as Nelson (op. cit.:200) intimated it might, the intergrades probably will be found along the Tonto Rim or in the territory between the Blue Range and the Graham Mountains.
Sylvilagus floridanus cognatus Nelson
1907. Sylvilagus cognatus Nelson, Proc. Biol. Soc. Washington, 20:82, July 22.
We have examined the specimens recorded by Nelson (N. Amer. Fauna, 29:193, August 31, 1909) and conclude that Nelson (op. cit.) accurately described them. We differ from Nelson on one point of interpretation; we prefer to use the trinomial, instead of the binomial, for cognatus because the kind and amount of difference between it and subspecies of Sylvilagus floridanus (S. f. holzneri and possibly S. f. llanensis) is on the order of magnitude that distinguishes subspecies, and not full species, of Sylvilagus.