1905. _Lepus pinetis robustus_ V. Bailey, N. Amer. Fauna, 25:159,
October 24.
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
([female] 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 floridanus
robustus_.
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.