8 



equally remarkable tliat the latter also contain the 

 thinnest and most fragile as well as the most ponder- 

 ous species. 



Durinc^ a recent journey through Georgia and 

 Alabama, I was enabled to learn the western limits 

 of that class of shells of which Unio purpureus of 

 Say may be considered the most characteristic. 

 They occur in the Savannah, Oconee and Ocmulgee. 

 but there they terminate, as Fhnt river, the first 

 tributary of the Gulf of Mexico, which I crossed in 

 my route, furnishes plicated shells and species iden- 

 tical with some inhabiting the Ohio. I have not 

 examined any of the rivers intermediate to the Flint 

 and Ocmulgee, but as these two are only thirty miles 

 distant from each other, and are not divided by a 

 range of mountains, I think the fact that the Ocmul- 

 gee contains the "eastern" and the Flint the "west- 

 ern" species, substantiates the theory I have for 

 years indulged, that the shells of the Atlantic streams 

 differ in their general character from those of all the 

 waters which flow into the Gulf of Mexico. I must 

 observe, however, that a shell which I believe to be 

 I'nio purpureus, occurs in Flint river, in company 

 with the ponderous and plicated shells, but west of 

 this I never observed the species. A variety of U. 

 decUvis, Say, was found in East Florida by Dr. 

 Ijlanding, and U. parvus, Barnes, it is said, also 



