4 THE ELEMENTS 



are called porcelanaceous shells. To 

 this class belong various species of 

 conus, cypra3a, voliita, &c. 



The second class consists of shells 

 generally covered w^ith a strong epi- 

 dermis or skin, below^ which lies the 

 shell in layers, and composed entirely 

 of the substance well known by the 

 name of mother-of-pearl. In this class 

 are the fresh-water muscles, (the my- 

 tilus cygneus and anatinus of Linne), 

 the haliotis iris (called the ear-shell}, 

 the turbo olearus, and several of the 

 trochus tribe, &c. 



The porcelaneous shells, contain a 

 very small portion of soft animal mat- 

 ter; and those of the second class a 

 very large proportion.* 



It must be clearly understood, that, 

 all shell-Jish are not included in the 

 science of Testaceology.f- The crabs, 



* See Thomson's System of Chemistry, vol. v. page 507, &c. 

 t Testaceology, is a modern term for the Natural History of 

 chells, and synonymous with Conchology. 



