PREFACE. Vll 



In the observations appended to the characters of 

 groups and species, there is added, as opportunities 

 occurred, a physiological account of the mode of for- 

 mation and structure of the different parts of shells.* 

 It is to this part of the subject that I would especially 

 direct the attention of my readers ; as, in the study 

 of the structure, formation, developement, and colour- 

 ing of the shells, and in the habits of the animals 

 which form them, they will find a never-failing 

 source of pleasure and instruction, which can be 

 carried on without any expense. For these parti- 

 culars are as easily to be observed in the most 

 common snail, as in the finest and most expensive 

 shells in the cabinets of the curious ; and the details 

 are more easily followed out, from the very fact of 

 the facility of observing many specimens at the same 

 time, in different states of developement : so that, to 

 the philosophical conchologist and reflecting stu- 

 dent, the most common specimens may do more 

 to illustrate the perfection and all-seeing wisdom 

 of the Creator, than the most costly collection. In 

 the description of the species, particular attention has 

 been paid to dividing them into small groups, to 

 facilitate their determination; and an attempt has 

 been made to point out the different varieties that 

 occur, not by describing each individual variety that 

 may be found, but by indicating the points that have 



* For a larger exposition of my views on this subject, refe- 

 rence should be made to papers published in the Philosophical 

 Transactions for 1833, and in the first volume of the Zoological 

 Journal. 



