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_.
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.