VII. 
OF THE INTRODUCTION OF FOREIGN SPECIES INTO THE 
UNITED STATES. 
TnE frequent commercial intercourse subsisting be- 
tween various countries is producing, slowly but surely, 
important changes iu the fauna of many districts ; and 
must presently render it difficult to distinguish their in- 
digenous animals from those tbat have been imported. 
Nowhere is international commerce more active, than 
between the western and southern nations of Europe and 
the United States ; and hence we are peculiarly liable to 
the introduction of animals from that part of the world. 
Considerable additions to our catalogues of the lower 
animals, particularly of insects, have already been made 
in this way, and it has therefore become desirable, that 
an accurate determination of our native species, in every 
department, should be had, previous to any further in- 
crease from this source. For this reason, we have 
endeavored to ascertain the facts relating to tin; intro- 
duced species of land-shells, whether derived from tins 
source or others, both for the interest connected with the 
