INTRODUCTION. 
XHE principal object of the present Catalogue has been, 
to give a complete list of the species of Mollusca which 
have been recorded as found in Great Britain, indicating at 
the same time the peculiarities of the specimens in the 
Museum Collection, as regards state, habitation, condition, 
and the source from whence they have been derived. 
The synonyms have been given to the various divisions of 
the class, and to the genera and subgenera and the species, 
and a reference is made to the works in which they have 
been characterized and described ; and some attention has 
been paid to the date at which the works appeared, to 
show the priority of publication of the various names and 
groups. 
It has been considered desirable, wherever it was possible, 
to use the first name which has been given to the various 
classes, orders, genera, and species. As far as regards the 
specific name, there is comparatively little difficulty in the 
application of the simple rule of priority ; but ordinal, and 
especially generic names have been used by different authors 
in senses so widely different, and the groups which they are 
intended to designate have been so variously extended and 
restricted, that it is no easy matter to determine, where 
