OVERLAPPING AREAS. 23 



timidus, var. Arcticus), whose range extends from the Arctic coast 

 southward to Newfoundland, and in the interior to Fort Churchill, 

 on Hudson's Bay. Along its southern confines it meets and slightly 

 overlaps the boundaries of the northern varying hare (L. Ameri- 

 canus), which, in its several geographical varieties, is distributed 

 from the Barren Grounds in the north southward to a zone which 

 corresponds generally with the isotherm of 52° F. On the Atlantic 

 coast region, the southern limit of this species appears to be Con- 

 necticut ; along the line of the Appalachian highlands, Virginia (or 

 possibly North Carolina) ; and in the Rocky Mountain region, New 

 Mexico. Lepus Americanus is found throughout the northern parts 

 of nearly all the northern tier of States interposed between the 

 Missouri and the Atlantic coast, and over the greater portion of 

 this vast area of distribution, which is con'tinued westward to the 

 Pacific, it forms the sole representative of the family. In the 

 south its habitat overlaps the range of the wood-hare (L. sylvati- 

 cus), which, in its several varietal forms, is distributed along the 

 Atlantic coast from Southern New England to Yucatan. West- 

 ward, the range of this species extends quite, or very nearly, to the 

 Pacific, keeping, however, to a course south of the isotherm of 

 45° F. The prairie-hare (L. campestris) is found in the interior 

 region, principally between the isotherms of 56° and 36°, its range 

 being consequently overlapped on the north by that of Lepus 

 Americanus, and on the south by L. sylvaticus. In the South- 

 eastern United States there are two distinct species, L. palustris 

 and L. aquaticus, which are almost exclusively confined to the 

 marshy lowlands, and whose habitats, extending to Yucatan on 

 the south, are partially comprised in those of the wood-hare and 

 jackass-hare (L. callotis), the last a western species, whose range 

 descends into the arid interior of the Republic of Mexico. Finally, 

 we have a solitary species of South American hare (L. Brasiliensis), 

 whose reputed range embraces a considerable portion of the con- 

 tinent from Patagonia to Panama, continuing thence into Central 

 America.^ 



It frequently happens that the boundaries of a given species are 

 sharply. defined against those of another, stopping just where the 

 others begin, and where, consequently, no overlapping takes place. 

 Such cases of specific Ihnitation occur where natural obstacles to a 

 free migration are suddenly encountered, as where mountain or 



