MUSEUM OF COMPARATIVE ZOOLOGY. 203 



minusculus, fulrus, indebitatus, Helix pulchella, H Hneata, Patula 

 striatella, Cionella subcyHndrica. 



Helix Rowelli, a Lower California species, is omitted from the list, its 

 presence in Arizona not being well authenticated. 



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

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

 its genera and subgenera being the same, excepting Polyyyrella, its only 

 peculiar subgenus of Helix. It may therefore be of the same origin 

 as the fauna of the Eastern Province. 



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

 of its climate and soil, — causes in equal force on 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 ;he (a) 

 Northern Region, (b) the Interior Region, and (c) the Southern Region. 



(a.) The Northern Region f .comprises the whole northern portion 

 of the continent, including Greenland and Alaska. Its southern 

 boundary is not perfectly known, and probably not exactly marked ; it 

 may, however, be indicated in general terms as the same with the polit- 

 ical division between the British Possessions 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 



* 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. 



t F'or a description of this Region, see A. Binncy, 1. c. pp. 124, 125, under sections 

 5 and 6. 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. 



