6 INTKODUCTION. 



vations, depressions, strise, 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 

 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 



