26 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



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

 Territories. 1 



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) Northern 

 Region, (6) the Interior Region, and (c) the Southern Region. 



(a.) The Northern Region 2 comprises the whole northern portion of 

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

 dary 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 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 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, 8 especially small Zonites, which are able to bear the severe 

 climate of the north. 



The following are the species of the Northern Region : 



Vitrina limpida. Zonites multidentatus. 



Angelicas. Patula striatella. 



exilis. asteriscus. 



Zonites fulvus. pauper. 



nitidus. Acanthinula harpa. 



viridulus. Vallonia pulchella. 



Fabricii. Ferussacia subcylindrica. 



milium. Pupa muscorum. 



Binneyanus. Blandi. 



ferreus. Hoppii. 



exiguus. decora. 



1 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.) 



2 For a description of this Region, see Vol. I. 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. 



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

 the Interior Region. 



