INTRODUCTION. 



The term " Conchology,^^ in its legitimate usage, is applied to 

 that department of Natural History which has reference to ani- 

 mals with testaceous covering or shells. It is not unfrequently 

 confounded with Crustaceology, but the distinction is obvious 

 and radical, lying not more in the composition of the animal's 

 habitation, than in the organization of the animal itself. This 

 latter, in the Crustacea, is of a fibrous nature, and has articulated 

 limbs ; the shell, strictly adapted to the members, covers the crea- 

 ture like a coat of mail, is produced at one elaboration, is cast or 

 thrown aside periodically, and, again at one elaboration, renewed ; 

 it is moreover composed of the animal matter with phosphate of 

 lime. In the Testacea, on the contrary, the inhabitant is of a 

 simple and soft texture, without bones, and is attached to its 

 domicil by a certain adhesive muscular force ; this domicil, too, 

 is a permanent one, and is increased, from time to time, by 

 gradual additions on the part of the tenant ; while the entire 

 shell, which is distributed in layers, or strata, is a combination of 

 carbonate of lime, with a very small portion of gelatinous matter. 

 Such animals, then, with such shells, form, alone, the subject of a 

 proper " Conchology." 



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