VI 
PREFACE. 
The remains of Shells are sometimes so well pre- 
served that many recent ones are not equal to them, 
either in preservation or beauty, and it often happens 
that the peculiar nature of their situation preserves 
them in a manner that excels all our art in repre- 
sentation. The pearly lustre is, in some, even 
superior to that of the most recent Shells, and 
the changes into Carbonate of Lime with the crystal- 
lized structure, into Flint, Calcedony, &c. are 
generally such as to excite our admiration; every 
minutia being so well cast as to preserve the most 
attenuated striae or elaborate markings; and even 
the polish and colour are often admirably retained, 
and additional splendour gained under ground, by 
means of Sulphuret of Iron, giving a metallic 
lustre which equals, if it does not surpass every 
thing else. 
It is thought that Generic names of Shells, with- 
out the termination lites or ites, to signify the stony 
substance of which they consist, as Nautilus, not 
Nautilites, are preferable, as it often happens that 
the slight change Shells have undergone may not 
warrant them, and the cast shewn may be considered 
quite inconsistent with such a term. The description 
will say in general what change a specimen may have 
