9G 



INTRODUCTION. 



This classification is better exLibitecl in tlie following 

 tabular form : 



As the immediate subjects of this work are com- 

 prised within one section of the pneumo-branchiate 

 mollusks, namely, that contauiing the species living 

 upon the land, it will not be necessary to give any ac- 

 count of the order as a whole, beyond that contained 

 in the preceding definition, except to indicate such of 

 our native genera, as are by the best authorities ad- 

 mitted into it, and their natural groupings into fami- 

 lies. Tliis is done in the following tabular view. It 

 is proper, however, to notice, that there is much reason 

 to doubt whether the family of Auriculadce is truly 

 pneumo-brancliiate, and that the characters of the 



