A MANUAL OF AMERICAN LAND SHELLS. 41 



three continents has facilitated tlieir distribution. In this connection 

 it is worthy of note that one of our existing species, now confined to 

 America {IStrobila lahyrinthica), is said to have existed in France in 

 Tertiary days. 



Our Southern Eegion has evidently been peopled from some other fauna 

 than that which supplied the Mesodon, Triodopsis, Stenotrema, &c., of 

 the Interior Eegion. It was, no doubt, from some now extinct semi- 

 tropical fiiuna that these came, but long enougli ago to allow the Poly- 

 gyras, Gkmdinas, &c., to be modified into species distinct from those 

 which from the same common origin have become the equally well- 

 established West Indian, Central American, and Mexican species. 



The Central Province has, from geological causes, been more recently 

 peopled hj pulmonata than the Eastern Province. Its local species are 

 less numerous. Patula is its characteristic genus, with species so vary- 

 ing and intermingling one with the other, that the student cannot 

 refrain from noticing that they have the a^jpearance of a species in a 

 slightly advanced stage of evolution, each form not as yet established 

 as distinct, easily-recognized species. 



The Pacific Province also presents in its variable, scarcely distin- 

 guishable Ariontas, a fauna of comparatively recent growth, but whence 

 its origin it is difficult to say.* 



Finally, we have in the list of American land shells several species 

 purely local in their distribution, imported through the more or less 

 direct agency of man. Of these, Fomatia aspersa was no doubt intro- 

 duced as an article of food by foreign residents of Charleston, S. C, and 

 seems to have established a hold there.f Zonites cellarius was intro- 

 duced by foreign shipping, probably around water-casks. It is also well 

 known to have been introduced into other countries. The Limaces 

 are found around human habitations ; they seem to follow the English 

 to all their colonies. The other foreign species mentioned on p. 28 

 have probably been introduced around the roots of plants, as have been 

 other species which are from time to time sent me from greenhouses, 

 gardens, &c. They are only local, except Tachea hortensis, which may 

 have been accidentally introduced in some other manner, since the dis- 

 covery of America by Europeans, and owes its present distribution in 



* See Dr. Cooper, as referred to ou p. 19. 



tl have been asked what authority I have for this opinion, so think it worthy of 

 st.n-teinent that Charleston specimens belonging to the cabinet of the late General 

 Totten still retain the odor of the garlic with which the animal was cooked. French 

 residents of Philadelphia have been known by me to purchase them as food. 



