VI PREFACE. 



indebted to the invaluable work of Moquin-Tandon, 

 entitled " Histoire naturelle des Mollusques terrestres 

 et fluviatiles de France/^ in which the physiology and 

 anatomy of the land and freshwater Mollusca have been 

 treated in a far more able and exhaustive manner than 

 had been previously done by any author. 



My old and esteemed friend, Mr. Alder, has most 

 kindly promised to assist me with a notice of the Nudi- 

 branchsj so as to make that part of the subject as com- 

 plete as possible ; and the value of such cooperation will 

 be fully appreciated by all naturalists. 



A volume of supplementary plates will probably be 

 published, to contain figures of every species and well- 

 marked variety. The figures now given illustrate the 

 genera ; but the cost and price of the work would have 

 been greatly increased by the other mode of illustration, 

 except by resorting to the inartistic and unsatisfactory 

 substitute of woodcuts. 



In the prosecution of this task I have been actuated 

 by what I trust mil not be deemed a selfish consideration. 

 The study of our native Mollusca has been to me fi'om 

 childhood such an inexhaustible source of pleasant and 

 innocent occupation, it has given me so many happy 

 hours, and it has taken away or alleviated the sting of 

 so many sorrows, that I am desirous to assist in making 

 it more an object of general cultivation than it has 

 hitherto been. This field of research has by no means 

 been exhausted ; and whether regarded in a zoological 



