7 
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 two 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; but 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 greatlakes contain some of those 
species of Naiades, which inhabit the Ohio, and the 
Unio cardium, Raf. U. inflatus, Barnes, and U. ala- 
tus. Say, have been found in Lake Champlain, 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 acknowledged 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 they are distinct. It is 
remarkable that our eastern waters do not furnish a 
single tuber culated, alated or plicated bivalve, and 
the species are thin compared with the greater 
number of those in the western waters. Yet it is 
