VI PREFACE. 



Association, at Birmingham, his Report on this sub- 

 ject, which (judging from the abstract of it that was 

 read at the meeting, and has since been printed in 

 the Athenaum,) will doubtless contain much additional 

 information. The Introduction also contains, 4thly, 

 an account of the fossil species which formerly in- 

 habited this country ; 5thly, the situations generally 

 preferred by different species of shells ; 6thly, an out- 

 line of the history of the various additions that have been 

 made, from time to time, in this part of our Fauna ; 

 and, lastly, a catalogue of the works and papers which 

 treat on British land and fresh-water mollusca, and 

 of the best works on European species. 



For the purpose of assisting the young student, or 

 those who study the mere shell, without paying any 

 attention to the animals that form them, an arti- 

 ficial table of the genera has been framed, and to it 

 is appended a definition of the more important and 

 general terms used in the description of shells ; some 

 of which have, until lately, been employed in different 

 senses by even celebrated authors. The description 

 of the species is preceded by a general outline of the 

 distribution of molluscous animals; and the genera 

 have been distributed into natural families from cha- 

 racters taken from the consideration of the animal, 

 which alone can be regarded as the proper subject 

 for classification. Every day proves, to the scientific 

 conchologist, that every modification in the structure 

 of the animal impresses its character on the shell, 

 and that the shells thus afford good subsidiary cha- 

 racters for the distinction of groups. 



