X PREFACE. 



species, I have followed the practice of some botanists, 

 and given only the generic character, believing it to be 

 impossible, before a second species is discovered, to know 

 which characters will prove of specific, in contradistinction 

 to generic, value. 



In accordance with the Rules of the British Associa- 

 tion, I have faithfully endeavoured to give to each species 

 the first name attached to it, subsequently to the intro- 

 duction of the binomial system, in 1758, in the tenth 

 edition* of the ' Systema Naturae.' In accordance with 

 the Rules, I have rejected all names before this date, 

 and all MS. names. In one single instance, for reasons 

 fully assigned in the proper place, I have broken through 

 the great law of priority. I have given much fewer 

 synonyms than is usual in conchological works ; this 

 partly arises from my conviction that giving references 

 to works, in which there is not any original matter, or 

 in which the Plates are not of a high order of excellence, 

 is absolutely injurious to the progress of natural history, 

 and partly, from the impossibility of feeling certain to 

 which species the short descriptions given in most works 

 are applicable ; — thus, to take the commonest species, the 

 Lepas anatifera, I have not found a single description 

 (with the exception of the anatomical description by 

 M. Martin St. Ange) by which this species can be 

 certainly discriminated from the almost equally common 

 Lepas Hillii. I have, however, been fortunate in having 



* In the Rules published by the British Association, the 12th edition, 

 (17C)6,) is specified, but I am informed by Mr. Strickland that this is an 

 error, and that the binomial method was followed in the 10th edition. 



