INTRODUCTION. XVII 



On the Colours of Shells, and the Formation of their 

 Streaks and Spots, 



The first thing which presents itself to the Con- 

 chologist is the colours of shells, which may justly 

 be admired, both for their beauty and variety. 

 Nature seems here to have diversified her operations, 

 in every way possible ; some are distinctly spotted, 

 others streaked; in some the bands are uninter- 

 rupted, in others they are broken into parts, so as 

 to bear a slight resemblance to the notes of musick. 

 Again we meet with shells, where the tints are 

 partly distinct, and partly melted together, or 

 formed, as it were, into clouds. What is the oc- 

 casion of all this diversity, and how is it produced ? 



When a hole is made in a shell, at about midway 

 between the summit and the mouth, the new piece 

 which the animal supplies is generally of a whitish 

 colour, and often very different, in appearance, 

 from the rest of the shell ; whence we may conclude 

 that it is not made precisely in the same manner. 

 To clear up this difficulty, it will be necessary 

 to ascertain how this regular variety of colour 

 is produced. We shall take, for an example, the 



