TERRESTRIAL AIR-BREATHING MOLLUSKS 

 OF THE UNITED STATES. 



I. HABITS AND FACULTIES. 1 



The animals of this order, indigenous to the United States, are essen- 

 tially inhabitants of the forest. It is there, under the deep shadows of 

 a dense foliage, where the sun's rays hardly penetrate to the surface of 

 the earth, and where the ground is covered with the mouldering trunks 

 of trees and thick layers of decaying leaves, that they find a constant 

 moisture, a twilight interrupted only by darkness, abundance of vegeta- 

 ble and animal food, and the means of shelter and protection. These 

 constitute a combination of circumstances very favorable to their in- 

 crease, and hence they may be discovered, in situations where these con- 

 ditions exist, in every part of the country where they can be found at all. 

 But when, with these, are conjoined a mild climate and a calcareous 

 soil, the maximum of favoring influences is reached, and large numbers 

 are produced. It is in the great valley of the Mississippi, based through- 

 out nearly its whole extent upon horizontal limestone formations, that 

 these combined causes operate over an extensive region, and there, con- 

 sequently, the species proper to it exist in multitudes. In the parts of 

 the country which have been long cultivated, and are nearly deprived 

 of their forests, they have mostly disappeared, and only survive in 

 places where some shelter of wood or stones is still afforded to them. 

 They everywhere avoid cultivated fields and open pastures, and are 

 never found in gardens, 2 or about or within houses or other buildings, 



1 I have reproduced Chapter X. of Vol. I., adding to and modifying it in several par- 

 ticulars when required by my more recent experience and investigations. 



2 I have in the text already modified this assertion of my father. The instance he 

 gives in his note of "an exception to this remark in Helix fallax, Say (= Hopetonensis), 

 which we observed a few years since living in great numbers in gardens in Charleston, 

 S. C, in company with Bulimics decollatus," is by no means single. In every country 

 town and even city some species is sure to be found numerous in gardens and especially in 

 cemeteries, and once having gained a foothold bids fair to retain it. In Burlington, N. J. 



VOL. IV. 1 



