PREFACE. 



This volume, prepared at the request of the Smithsonian In- 

 stitution, is devoted to all the operculated land and fresh-water 

 mollusks of North America, excepting the family of Melanians. 

 The descriptions of the Cyclophoridse, Truncatellidse, and Eeli- 

 cinidx have already been published in the " Terrestrial Mollusks 

 of the United States," Vols. 2 and 4. It will be seen, however, 

 that these families are now grouped according to their lingual 

 dentition and breathing organs, and not collectively as Pneu- 

 monopoma. In treating the fresh-water families, it has been 

 considered better to give the original description, or an English 

 translation of it, and a fac-simile in outline of the original figure 

 of each species and synonym. This work must, therefore, be con- 

 sidered rather as a report on the present state of our knowledge 

 of the subject. When the large area over which the species 

 range shall have been explored and full suites of specimens 

 obtained of every age, variety and locality, and when this volume 

 shall have elicited criticism and prompted research, a complete 

 monograph may then be prepared on the decisions of which the 

 student can fully rely as correct. 



An extensive correspondence with all the living American 

 conchologists, and opportunities of examining the original speci- 

 mens from which the descriptions of almost all the species were 

 drawn, have enabled me to eliminate from the list of species a 

 large number of synonyms. The original description and figure 

 of these being given, the student can judge for himself of the 

 correctness of my conclusions. 



The descriptions of families and genera of the Viviparidse and 

 Eissoidse are adopted from Dr. Stimpson, those of the former 

 from his manuscript, of the latter from a paper entitled '' Re- 

 searches on the Hvdrobiinaj and Allied Forms," lately published 



( iii ) 



