18 A MANUAL OF AMERICAN LAND SHELLS. 



other convenieut place. A considerable number of separate deposits 

 are made during the year. 



II.— GEOGEAPHICAL DISTRIBUTION. 



I cannot too strongly urge, in extenuation of the imperfection of this 

 chapter, the meagerness of the data on which some of my views are 

 founded. I may say with exact truth that the Coast Range counties of 

 California, New England, and the States north of the Ohio River are 

 the only ones which have been thoroughly searched. The species of the 

 rest of the country are known only by the researches of few and widely 

 separated resident naturalists, from the collectors sent by my father, 

 and by collections made by my correspondents while traveling in vari- 

 ous sections of the country. The last sources of information are re- 

 stricted to purely accidental localities. There has been no systematic 

 investigation of vast tracts of intervening country or of some very im- 

 portant points. 



The subject must be studied in connection with the chapter on the 

 same subject in Vol. I of Terr. Moll. F. S., p. 99. I need not add that 

 from the proper sources the studentof distribution must have a thorough 

 knowledge of the physical geography of North America. 



The limits of the fauna at the South correspond quite accurately with 

 the political limits of the United States. The Mexican fauna has lately 

 been investigated by Messrs. Fischer and Crosse in the exhaustive work 

 on " Les Mollusques Terrestres et Fluviatiles du Mexique et de I'Ame- 

 rique Centrale." The northern limit of the fauna is formed by climate 

 alone. Thus our limits comprise all the continent of North America, 

 from the extreme north to San Diego and the Rio Grande. 



Properly speaking, there are two distinct faunas within these limits, 

 the Pacific and Eastern, with perhaps a third in the Central Basin, but 

 for convenience they are all treated as part of the North American 

 fauna. I have therefore designated these as — 

 I. — The Pacific Province. 

 II. — The Central Province. 



III. — The Eastern Province.* 



* In the work of Wallace quoted Lelow, North America is designated as the Nearctic 

 region. The subdivisions proposed by him correspond almost exactly with my own. 

 Thus his Californian and Rocky Mountain Subregion are identical with my Pacific 

 and Central Provinces. His Canadian Subregion is about the'&arae as my North- 

 ern Region of the Eastern Province. His Alleghany Subregion includes both my 

 Interior and Southern Region of the Eastern Province. 



