200 MOLLUSCA. 



becomes exceedingly thin, and often dried and with- 

 ered. The shells of Testaceous Mollusca frequently 

 display great elegance of form, fineness of texture, 

 and brilliancy of colouring ; they always consist of 

 matter deposited in layers, and secreted from the 

 skin, on that surface next the interior of the body. 



The Mollusca are arranged in six Classes, accord- 

 ing to the various modification of their organs. 



