26 A MANUAL OF AMERICAN LAND SHELLS. 



The fauna of the Central Province is quite distinct from that of tlie 

 Pacific Province, but is nearly allied to that of the Eastern Province, 

 its genera being the same, excepting Polygyrella. It may, therefore, be 

 of the same origin as the fauna of the Eastern Province. 



The paucity of species over this large area is owing to the nature 

 of its climate and soil — causes in equal force ou the western border of 

 the Eastern Province. 



In order to avoid mistakes in the study of the geographical distribu- 

 tion of North American land shells one must constantly bear in mind 

 the changes in the names and boundaries of the trans-Mississippi States 

 and Territories.* 



III. — The Eastern Province comprises the remaining portions of the 

 continent north of Mexico. The species by which it is inhabited have 

 been derived partly from the north, partly from the interior, and partly 

 from the south. It may, therefore, be divided into the (a) iforthern 

 Region, (&) the Interior Region, and (c) the Southern Region. 



{a) The Northern Region t comprises the whole northern portion of 

 the continent, including Greenland and Alaska. Its southern bound- 

 ary is not perfectly known, and probably not exactly marked ; it may, 

 however, be indicated in general terms as the same with the political 

 division between the British jjossessions and the United States to the 

 northeast corner of New York, where it runs southwesterly along the 

 Appalachian chain of mountains to Chesapeake Bay, thus including 

 all New England, and the portions of New York, New Jersey, Penn- 

 sylvania, and Maryland lying east of those mountains. Into this south- 

 ern extension of the region we find the Interior Region overlapping, as 

 will be shown below while treating of the interior fauna. At other 

 points in the region also have been found species from the Interior 

 Region,! especially small Zonites, which are able to bear the severe 

 climate of the north. 



* Thus, Helix Mullani was described in Land and Freshwater Shells of North America, 

 I, 131, from points in Washington Territory and Oregon. Both localities are now in 

 Idaho. (1875.) "^ 



tFor a description of this region see Terr. Moll. U. S., Vol. I, pp. 124, 125, under 

 sections 5 and G. The American land shells, especially those of the Interior Region, 

 are forest species; they become rare towards the Northern Region of the continent as 

 the deciduous trees become rare. 



t See Proc. Phila. Acad. N. S., 1861, p. 330, for the northern range of species from the 

 Interior Region. 



