INTRODUCTION. 27 



According to Ferussac, 



Helix pulchella is the H. minuta of Say. 



Zonites nitidus is probably the H. arborea of Say. 



Say considered the 



Paludina vivipara of the two countries the same 

 species. 



Mr. Lea considers, I believe truly, that the 



Unio margaritifera of the two countries is the same 

 species. 



From the facility with which the land Mollusca 

 can be transported during their torpidity, there have 

 been introduced into Canada and the United States 

 the following British species : — 



Helix nemoralis. Canada and U. States. 



hortensis. Boston. 



aspersa. U. States. 



virgata. U. States. Ferus. 



Pisana. U. States. Ferus. 



Bulimus acutus. U. States. Lesueur. 



Bulimus decollatus has been introduced into gardens 

 near Charlestown, S. Carolina. One of the species, 

 H. aspersa, has also been introduced and naturalised 

 in Brazil and some places in S. America. 



The facility with which these animals migrate and 

 adopt a new country, as proved by the above instances, 

 by those cited at p. 4., and by the naturalisation of the 

 H. cantiana on the banks of the Tyne, will always 

 make the study of the geographical distribution of the 

 terrestrial Mollusca difficult. According to the ac- 

 counts of the American authors, the species which have 

 naturalised themselves retain their fondness for trees 

 and hedges and herbage, and keep themselves quite 

 distinct from the forest-living species of America. 



c2 



