Vlll PREFACE. 



admeasurement I have considered preferable to stating 

 the largest dimensions to which each species attains, 

 which would not give a fair idea of the usual size, or to 

 adopting the method used by some Continental authors 

 of giving the range or extreme limits of such dimensions. 

 Any extraordinary diflference of size presented by speci- 

 mens or varieties will be noticed. In giving the ad- 

 measurement of bivalve shells, I have considered the 

 length to correspond with the line of growth (viz. from 

 the apex or beak to the front margin), and the breadth 

 from one side of each valve to the other. In the case of 

 univalve shells I have adopted the same rule, viz. taking 

 the line of gi'owth for the length (the apex or point of 

 the spire representing each beak of the bivalve) , and the 

 widest part of the shell, or its greatest diameter, for the 

 breadth. 



At the end of the work I propose to give some prac- 

 tical hints to collectors. 



For the benefit of such of my lady readers as have not 

 added a knowledge of the classics to their other accom- 

 plishments, I have marked the accentuation of all the 

 names of genera and species described in this work. One 

 word of frequent occun^ence I have noticed to be too 

 often mispronounced by many who ought to know better, 

 and that is the specific name of our common eatable 

 oyster, mussel, and cockle. This word [edidis] has the 

 middle syllable long, as is evident by remembering one 

 of the various gastronomic maxims of Catius, "Vinea 



