6 Treface 



shell - collector's handbook that the volume is sent 

 forth ; rather to suggest the consideration of these 

 creatures as living organisms, whose diversity of 

 form and structure has intimate relation to their 

 mode of life, the persecution of enemies, and other 

 factors in the struggle for existence — though some of 

 us are at times too apt to regard such differences as 

 being dictated by the needs of the classifying 

 naturalist. In accordance with this intention, so 

 far as was compatible with the necessity for pro- 

 ducing a volume of handy size, attention has been 

 directed to those habits and external influences that 

 may reasonably be considered to have brought about 

 modifications of form and colour, protective resem- 

 blances, and so forth. 



A few words may be added as to the system upon 

 which the Genera, Families, and Orders have been 

 grouped (see Appendix). In this matter I have 

 mainly followed the plan adopted by the Rev. A. H. 

 Cooke, M.A., in his admirable "Molluscs" {Camhridge 

 Natural History, vol. iii.), which is likely to long 

 remain the standard text-book. The reader who 

 desires to enter upon the wider and deeper study of 

 this branch of Nature will thus experience no difl[i- 

 culty in expanding his elementary acquaintance with 

 our local fauna into a fuller knowledge of the 

 Mollusca of the world. 



