2(38 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 presenl 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 Leporidce 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 arc constitu- 

 tionally less susceptible to climatic influences, we certainly find a less degree 

 of geographical variation among the species of the Leporidce 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 Leporidce, 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 



