VI PREFACE. 



greater value, I acquired the habit of comparing 

 structure with structure, of marking minute dif- 

 ferences of form, and became in some measure 

 accustomed to that precision of language, without 

 which descriptive* natural history could not exist. 



I have endeavoured in the following pages to 

 furnish to the sea-side naturalist, what the Lin- 

 nean Genera Insectorum were to me. That such 

 a book is a desideratum, I need hardly say. Many 

 a time have I been asked to indicate some pub- 

 lished work, whereby the student who picks up 

 a shell from the beach, or a worm from under 

 stones at low water, may know what it is that he 

 has found. I might indeed point to the admirable 

 works of Yarrell, of Forbes, of Johnston, of Baird, 

 of Bell, of Busk, and others who have written 

 Monographs of particular classes or groups. But 

 this is not what is wanted ; — the information re- 

 quired is scattered through so large a number of 

 volumes, that a book-case needs to form a part of 

 the sea-side visitor's luggage. Moreover, to per- 

 sons of limited income the expense of these works 

 often forms an insuperable bar to their possession. 

 Thirty pounds would not purchase the books 

 necessary for the identification of the marine 

 animals of Britain ; while if this sum were ex- 

 pended, there would still remain gaps of awful 

 width, — whole Classes, for the recognition of 

 which no English hook is extant I need only 



