i 4 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
received from any locality, we find that variety Wuécadii finally not only differs 
markedly in its paler color from variety sy/vaticus, but also differs in being 
smaller; just as, in most cases among the mammals, the pallid forms of the 
arid plains and deserts prove to be also depauperate varieties of their 
brighter-colored and more favored or better-fed conspecific allies. 
Geographical variations in the relative size of the feet and ears as com- 
pared with the general size is not so easily determined from skins as is the 
difference in general size based on the size of the skull; and the only point 
in this connection that will be specially noticed is the lengthening of the 
ears to the southward, manifested by nearly all the species, the ears, in many 
cases, actually increasing in length while the general size diminishes. There 
is alsoa marked tendency to an enlargement of the ears in proportion to 
the aridity of the habitat. Thus, in the L. sylvaticus group, variety Nuttall 
has the ear generally quite appreciably larger than in variety sylvaticus, the 
maximum size of the ear being reached in the Great Colorado Desert in 
variety orizone, which is chiefly distinguishable from its nearest allies, varie- 
ties Nuttalli and Auduboni, by the enlargement of this member. L. cadlotis, 
LL. californicus, and L. Trowbridgei also show a very perceptible increase in 
the size and length of the ear to the southward. In this connection, also, 
attention may be called to the fact that all of the long-eared species of 
American Hares are found exclusively over the most arid portions of the 
continent; just as, in the Old World, all of the longest-eared species are 
fuund in the arid portions of Asia and Africa. 
The subject of geographical variation in size being quite fully discussed 
in connection with the detailed descriptions of the species and varieties given 
beyond, it is not necessary to devote further space to the subject here. 
II.— INDIVIDUAL VARIATION. 
The difference in size between specimens of the same age and sex from 
the same localities is often quite marked. The amount of this difference is 
sufficiently indicated by the subjoined measurements of skulls given in 
Table II. Care has been taken to select only fully adult specimens, and in 
the table only the maximum and minimum measurements are given. 
