ADVERTISEMENT. 
In this estimate, which the Author at first conceived 
would be completely adequate to every purpose of his 
design, he afterwards perceived himself in some degree 
mistaken. During the course of publication he has in 
various instances been kindly favoured with British Shells 
not before described: neither are the acquisitions which 
he has himself discovered in several remote parts of the 
country altogether unworthy of attention. Many of the 
species thus obtained were deemed too interesting to be 
omitted in a work of this nature, and it was therefore thought 
advisable to exclude those, which, from their extreme 
minuteness, are usually denominated Microscopic Shells, 
in order to admit the most important of them. ‘The 
omission of the more diminutive species, for the sake of 
inserting Shells of conspicuous figure, that had not been 
before described as English, the Author trusts will rather 
be considered as an advantage, than detriment to this 
work. Nothing of material consequence, either in the 
collection of the Author, or the cabinets of his friends, 
to which he has access, has been neglected in this selection ; 
and he could not feel himself completely justified in 
extending the work beyond the limits originally prescribed 
for no other purpose than to introduce the Microscopic 
Shells. 
