PREFACE. 



The Pulmonata are usually divided into Geoiohila, Limno- 

 phila, and Thalassophila, according as their habits are terrestrial, 

 fluviatile, or marine. The first division is included in the Land 

 and Fresh-Water Shells, Part I, now ready for the press. The 

 second and third divisions form the subject of the present volume. 



The descriptions of the family Auriculidse have already been 

 published in the fourth volume of The Terrestrial Mollusks of the 

 United States. In the other families I have adopted the plan of 

 giving the original description, or an English translation of it, 

 and a fac-simile of the original figure not only of each species, 

 but also of all those I have considered synonyms. I have thus 

 placed within the reach of every American student all the materials 

 for a complete monograph of the Lymuasidae, &c., of North 

 America which can be obtained from books. The other, more 

 important, source of knowledge of the subject can be gained only 

 by gathering together from every part of the country large suites 

 of specimens, fairly representing each species. Not until this is 

 done can their characters be described, and information given of 

 their variation, their geographical distribution, and their relations 

 to each other. 



Though not competent to prepare a monograph all whose de- 

 cisions may be considered final, it has been easy in numerous 

 cases to refer supposed new species to those previously described. 

 These instances arise from ignorance on the part of one author 

 of the labors of those preceding him, or in his exaggeration of 

 variations which to me have appeared too slight to denote .specific 

 difference. The repetition of the original description and figure 

 of each of these synonyms will enable the student to judge for 

 himself of the correctness of my decisions. 



The Museum Register printed after the description of each 

 species will show how large a collection of specimens I have had 



( iii ) 



