PROOF. Have the Jcindness to retiirn, with any corrections, to 

 W. G. Binney, Burlington, Neio Jersey, without delay. 



DESCRIPTIYE CATALOGUE 



OF THE SPECIES OP 



AMNICOLA, VIVIPARA, BITHYNIA, VALVATA, AND 

 AMPULLARIA, OF NORTH AMERICA. 



It is now twenty-two years since Prof. Haldeman eommencecl 

 the publication of bis " Monograph of the Fresh Water Univalve 

 Mollusca, of the United States," which must always remain the 

 standard work on the genera of which it treats. At that time 

 but little confusion existed in the synonymy of the few species 

 known, as among about thirty specific names given by him in the 

 genera Paludina, Amnicola, Valvata, and Ampullaria, but six 

 only were considered synonyms. He had also the advantage of 

 personal knowledge of all but one or two species, not only from 

 the fresh tradition of the collections, but generally also from 

 typical specimens of authors themselves. With these advantages 

 it was possible for him to prepare a monograph of these genera 

 on the decisions of which one could rely, as the most correct pos- 

 sible in that stage of conchological science. 



At the present time the case is very different. Instead of thirty 

 descriptions to study, we now have nearly one hundred and fifty. 

 They have been drawn from specimens received from isolated 

 situations, oftentimes by persons who have not had the advantage 

 of studying a large suite of individuals, or comparing typical 

 specimens, or even of access to the descriptions of others. The 

 shells belong to a class characterized, above all others, by a 

 remarkable range of variation, arising from local causes, different 

 stages of growth, or of station, &c. Many of them, at best, are 

 furnished with so few positive external specific characters, that we 

 can depend only for their determination on the discovery of some 

 anatomical differences. Indeed, it appears that to study satis- 

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