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 1905. _Lepus pinetis robustus_ V. Bailey, N. Amer. Fauna, 25:159, October 24.