PREFACE. 21 



The work contains descriptions of all the air- 

 breathing mollusks of the United States, living 

 upon the land, including both the aboriginal and 

 those foreign species which, having been from time 

 to time introduced, have now become naturalized 

 to the soil ; and of such species belonging to the 

 countries adjacent as are known to the author. 

 Our knowledge of these animals is brought down 

 to the date of publication ; and it is hoped that 

 the work will be found to be as complete as any 

 record of an actively progressive science can be. 

 In its preparation, all the American authorities 

 have been consulted, and for the benefit of Euro- 

 pean naturalists, some of whom appear to be 

 inexcusably ignorant or wilfully neglectful of 

 what has been done for Natural History in this 

 country, a catalogue of American authors, whose 

 works have been used in compiling these pages, 

 is given ; a catalogue of the foreign works, 

 referred to, is also added. A full synonomy of 

 the native species is attempted, and it will pro- 

 bably be found to be pretty complete ; but for 

 the introduced species a few references only to 

 well known works are given. 



Great care has been taken to investigate the 



