YII. 



OF THE INTRODUCTION OF FOREIGN SPECIES INTO THE 



UNITED STATES. 



The frequent commercial intercourse subsisting be- 

 tween various countries is producing, slowly but surely, 

 important changes in the fauna of many districts ; and 

 must presently render it difficult to distinguish their in- 

 digenous animals from those that 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 the intro- 

 duced species of land-shells, whether derived from this 

 source or others, both for the interest connected with the 



