Atlantic rivers form a striking* contrast; and it has 

 been a desideratum to discover where the line of" 

 demarcation has been drawn by nature in the south- 

 ern states, between these tv/o distinct races of shells, 

 and to fix with certainty the geographical limits of 

 the different species. The latter can only be effected 

 by years of patient observation; h'Y by contributing 

 such facts connected with the subject as may come 

 under our notice, we prepare the way for those who 

 may in future pursue the interesting inquiry with 

 more energy and zeal. 



It appears that the great lakes contain some of those 

 species of Naiades, which inhabit the Ohio, and the 

 Unio cardmm, Raf. U. infiatus, Barnes, and U. ala- 

 tus, Say, have been found in Lake Cham plain, yet none 

 of the tide waters of the Atlantic states contain either 

 of these species, nor any other of those denominated 

 "western shells." The Unio cariosus of Say is the 

 only acknoAvledged species common to all the waters 

 of the United States, although Alasmodonta margi- 

 nata of the Schuylkill is very analogous to a species 

 in the Ohio. Mr. Say, however, who is best qualified 

 to decide the point, thinks the' are distinct. It is 

 remarkable that our eastern waters do not furnish a 

 single tuberculated, alated or plicated bivalve, and 

 the species are thin '"omppred with the greater 

 number of those in the west, rn waters. Yet it is 



