X PREFACE. 



been compared with the specimens, and corrected 

 where required. There have also been added to 

 these plates other figures of the same species, and 

 enlarged details of those parts of the smaller kinds 

 which are calculated to facilitate the determination 

 of the species ; a short description of the animals, and 

 a few notes on their habits, have also been added ; 

 and this new feature in the work might have been 

 greatly extended, had it not been feared to add too 

 much to its bulk. Indeed, although this work has 

 been called in the titlepage a new edition of Dr. 

 Turton's Manual, it may be almost considered a new 

 publication, as the only portions of the former edition 

 that have been retained are the descriptions of the 

 species, and a few of the general observations ; inso- 

 much that, on revising it in its printed form, it is a 

 matter of regret to me, that it was not rather under- 

 taken as an entirely new work, Avhich would not 

 have cost me nearly so much trouble as editing the 

 present one. 



As an Appendix, there have been added, for the 

 purpose of assisting the young student, or those who 

 study the mere shells, without paying any attention 

 to the animals that form them, an artificial table of 

 the genera ; an outline of the history of the various 

 additions that have been made, from time to time, in 

 this part of our Fauna ; a list of the species which 

 I have reason to believe had been, from various 

 causes, erroneously introduced into works of this 



