238 MOLLUSCA. 



firmly fastened all round the edge of the shell ; stony 

 matter is now secreted and deposited by it layer 

 upon layer, and wherever the coloured glands are 

 placed there is a corresponding patch of colour. 

 Thus is the edge of the shell enlarged, and each 

 successive layer is thus painted at the moment of 

 its formation. The increase of the shell in thickness 

 is a subsequent process : the whole surface of the 

 mantle, except the collar, deposits a layer of pearly 

 matter upon the whole interior of the shell, includ- 

 ing the new part recently formed at the edge : and as 

 this portion of the mantle is destitute of colouring 

 glands, so the glassy surface of the interior shell is 

 nearly deprived of colour, except the opaline reflec- 

 tions which play over it in the changing light. The 

 projections of the ridged and spinous shells appear, 

 in like manner, to be formed by answering furrows 

 and depressions in the margin of the mantle.* 



In the genus, whose numerous and beautiful 

 species are so common in our cabinets, 



Cyprcea^ the Cowry, 



The mantle is remarkably ample, expanded into 

 two large wings, which fold over and envelop the 

 shell ; at certain periods of its age, a fresh layer is 

 thus deposited over the outer surface, varying in 

 colour from the preceding, and the long aperture 

 becomes wrinkled on each side in the adult, which 



* See Jones's Anim. Kingd. p. 420. 



f From KtJarg/;, lypris, a name of Venus ; on account of their beauty. 



