MONOGRAPH, &c. 



THE numerous fresh- water and terrestrial shells 

 which inhabit the interior of North America, had 

 not been observed nor described when I under- 

 took this task in the years 1818 and 1819. I was 

 surprised and delighted to find, that they were 

 nearly all new species, differing entirely from 

 those found in the vicinity of the Atlantic ; so 

 that it appears the chain of the Allegheny moun- 

 tains which divides the country, forms a distinc- 

 tive line between the fish and shells of the waters 

 of the Ohio and its tributaries, and those of the 

 rivers emptying into the Atlantic ocean. Though 

 very far from having exhausted the study of the 

 shells of this region, I have however observed 

 there, collected and figured, about one hundred 

 and eighty species; of these nearly seventy are 

 fluviatile univalves ; fifty terrestrial univalves and 

 sixty fluviatile bivalves. I now propose to de- 

 scribe the latter, the univalves will be described 

 elsewhere. I have already published many, and 

 particularly the new Genera, in my Prodromus 

 of the new animals of North America. 



The greater number of the bivalves of the Ohio 

 are found also in most of its tributary streams, 

 2 



