6 
INTRODUCTION. 
vations, depressions, striae, tubercles, spines, &c. 
which distinguish individuals in an almost infinite 
variety of contour, are to be attributed to corre- 
spondent projections, tentacula, and other irre- 
gularities in the fleshy form of the constructing 
1 agent. 
It is very important to the inexperienced col- 
lector to remark, that the young shells of many 
species present a very different appearance from 
that which distinguishes them when in a state of 
maturity. This difference has caused much con- 
fusion among naturalists, who were otherwise well- 
informed, and, in consequence, the same shells 
have sometimes been entered in their catalogues 
under several separate denominations. Not only 
is the painting altered in the new coats which are 
laid over the whole surface of the former ones in 
the progressive stages of their growth, but so com- 
pletely are they changed as not to bear the slight- 
est resemblance, except to a very scientific eye, 
either in the colours or in the distribution of them. 
The form varies so essentially as often to deceive 
the most expert Conchologist, and it is indeed 
