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

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.

The specimen (W.D. Hollister, original No. 208) from the Datil Mountains, lent to us by the Colorado Museum of Natural History, does have, as Nelson (op. cit.) pointed out, larger tympanic bullae and a slenderer rostrum than do other specimens of S. f. cognatus. Nevertheless, No. 208, agrees with cognatus and differs from Sylvilagus nuttallii pinetis in the greater vertical depth of the zygoma, the greater transverse width of the first pair of upper incisors, the broader posterior extensions of the supraorbital processes, the fusion (instead of freedom from, or mere touching to, the braincase) of the tips of these extensions, the less upturned supraorbital processes, and the more nearly truncate posterior margin of the supraorbital shield. Therefore, the specimen is referable to Sylvilagus floridanus cognatus. The slender rostrum and large tympanic bullae of No. 208 are either individual variations or features peculiar to the population of Sylvilagus floridanus in the Datil Mountains.

Sylvilagus floridanus robustus Bailey

Nelson (N. Amer. Fauna, 29:194–195, August 31, 1909) described specimens from the Big Bend area of Texas. This was the only area from which Nelson had specimens. Our examination of these same specimens indicates that his description of them was accurate. Davis and Robertson (Jour. Mamm., 25:271, September 8, 1944) recorded a specimen, under the name Sylvilagus robustus, from "The Bowl, Guadalupe Mountains, Culberson County, Texas." Our examination of the skull of this specimen (♀ adult, No. 658, Mus. Zool., Louisiana State University) indicates that it is, among named kinds of rabbits, best referred to robustus. The specimen is morphologically as well as geographically intermediate between S. f. cognatus and S. robustus. This morphological intermediacy is illustrated by certain of the following cranial measurements of three adult females: No. 108695 (robustus), Chisos Mts.; No. 658 from the Guadalupe Mts.; and No. 128651, NE slope Capitan Mts. Basilar length, 59.2, 54.2, 54.4; length of nasals, 33.9, 31.1, 32.2; breadth of rostrum above premolars, 19.3, 17.5, 17.0; depth of rostrum in front of premolars, 15.8, 14.8, 14.0; interorbital breadth, 20.4, 19.1, 19.7; parietal breadth, 27.2, 27.1, 26.5; diameter of bulla, 13.3, 12.2, 10.7. Considering the intermediate nature of specimen No. 648, and the kind and amount of difference between Sylvilagus floridanus cognatus and S. robustus, it seems appropriate to us to use the name-combination Sylvilagus