PORCELLANEOUS SHELLS. 



109 



and the teeth become apparent ; but the substance is 

 still thin, the colour faint, and the markings indistinct. 

 But in its third and perfect state, the cyprea has re- 

 ceived an additional coating of testaceous or shelly 

 matter, the pattern appears with its vivid tints and de- 

 licate markings, and the spire, 

 if not entirely hidden, yet 

 scarcely projects out of the 

 body. The animal itself under- 

 goes a considerable change in 

 appearance during its growth ; 

 its mantle at first is small, 

 but increases with its age, and 

 expands at the sides into two 

 ample wings ; and from these 

 is deposited the final layer, 

 which completes the shell. 

 This new plate completely 

 envelops the original shell, 

 giving it a new covering, and 

 disguising its former character. 

 A transverse section, shows the 

 steps by which these changes 

 have taken place. 



The shape of the shell de- 



