1CA 
INTRODUCTION. 
The whole number of species hitherto ascertained, 
within the bounds of the United States east of the Mis- 
sissippi River, excluding species found elsewhere also, is 
ninety -nine. 
The first reflection that arises, on examining this table, 
is, the comparatively small number of species which it 
exhibits. The number inhabiting the corresponding cli- 
matal parts of Europe, of equal territorial area, is more 
than twice as great ; and the limited extent of the British 
Islands affords at least an equal number. This in- 
equality of numbers may perhaps be partly explained by 
the supposition, that many species remain yet undiscov- 
ered ; but, considering the attention which has already 
been given to our conchology, we can hardly expect that 
the whole difference shoidd be made up by future re- 
searches. A further approximation of numbers may 
also be gained by cutting off some of the nominal species 
of European Limaces, which seem to be established on 
very slight external characters, and will hardly maintain 
their places; but when this is done, the difference 
remaining will still be very considerable. We confess 
that we do not perceive the means of reconciling the 
disparity of distribution, which strikes us as the more 
remarkable, because the species live in this country 
more in their natural condition than they can do in the 
cultivated parts of Humpe, and because a large portion of 
our territory seems to be, by its climate and geological 
structure, and other physical circumstances, peculiarly 
adapted to their growth and increase. The only circum- 
stance which we perceive, wherein the European local- 
