268 MONOGRAPHS OF NORTH AMERICAN RODENTIA, 
Mr. B. R. Ross, Mr. R. McFarlane, and other officers of the Hudson’s Bay 
Company. The most important collections from localities south of the United 
States are those made by Prof. F. Sumichrast in Southeastern Mexico, by 
Mr. C. A. Schott in Yucatan, and by Prof. W. M. Gabb in Costa Rica. 
As an indication of the amount of material that has been used in the 
preparation of the present memoir, it may be stated that of Lepus americanus 
(including its several varieties), the series of skulls alone numbers about one 
hundred and fifteen, which is supplemented by about the same number of 
skins; of Lepus sylvaticus and its varieties, the skulls number seventy, and 
the skins about one hundred and fifty, representing in each case, of course, 
a wide range of localities. 
Among the results reached by the elaboration of this large amount of 
material is a better understanding of the character and amount of the varia- 
tion dependent upon locality. These results, together with the data on 
which they are based, are presented with considerable detail in the following 
pages. 
I.— GEOGRAPHICAL VARIATION. 
Since most of the American Leporide are not only mainly nocturnal in 
their habits—living concealed in shaded places, as under fallen trees, thick 
bushes, or even in burrows during the day—but also live mostly in swamps, 
thickets, or forests, they are in a measure shielded, it would seem, from the 
climatic influences that produce so marked an effect upon animals having 
different habits and affecting more exposed situations. Whether or not these 
conditions have a tendency to reduce the variation with locality due to climatic 
conditions to a minimum, or whether the species of this group are constitu- 
tionally less susceptible to climatic influences, we certainly find a less degree 
of geographical variation among the species of the Leporide than among 
many other families of mammals. A considerable amount of variation, 
resulting from conditions of environment, however, exists among them, and 
conforms to the general laws of geographical variation previously announced 
as obtaining among both the mammals and birds of this continent. 
Among the Leporida, cases of melanism are of rare occurrence, less than 
half a dozen instances being as yet known to me. among our native species. 
Albinism, in its true sense, seems almost equally rare, since the regular assump- 
tion of a white winter pelage by the northern species can hardly be regarded 
as true albinism. Generally speaking, too, the variation in intensity of color 
