556 



[Feb. 26. 



Miocene Species oj Forms peculiar to America. 



While the analogy of the American and European miocene 

 shells is so striking, there are also some species of forms quite 

 peculiar to America ; e. g.-. — 



1. Oliva idonea. 



2. Fusus quadricostatns Say. 



3. F. sulcatus. 



4. F. parilis Con. 



5. Pyrula (Fulgur) carica Say. 



6. P. canaliculata Say. 



7. Calyptraa costata (C. ramosa Conrad). 



8. Gnathodon Grayi. 



9. Venus Tridacnoides. 



10. V. mercenaria Lam. 



1 1 . Modiola glandula Totten. 



1 2. Pecten magellanicus Lam. 



The six species in italics in the above list are recent, and are 

 confined to the western side of the Atlantic, and these characteristic 

 forms imply that the beginning of the present geographical distri- 

 bution of mollusca dates back to a period as remote as that of the 

 miocene strata. It will be also seen that several of the 23 miocene 

 shells identified with recent species in the list p. 419-20. are now 

 inhabitants of the American side of the Atlantic. 



On the other hand, when we examine the fossil shells of the 

 European miocene strata, we find most of those which are identi- 

 fiable with living species to belong to the British seas, to the 

 Mediterranean, or to the coast of North Africa, and not to extend 

 to the American side of the Atlantic, a fact which may be illus- 

 trated by the following list of species. 



European Miocene Shells found living on the Eastern, and not 

 inhabiting the Western, Side of the Atlantic. 



_No one of the above shells is found fossil in the American 

 miocene strata, and this fact strongly confirms the opinion before 

 stated respecting the high antiquity of the separation of the 

 existing molluscous faunae, which we see may be traced back to a 

 period when about four fifths of the species differed from those 



