CONCHOLOGIA CESTRICA. 



THE MOLLUSCA. 



THE term Mollusca, or Mollusks, is applied to a 

 numerous division of the animal kingdom, com- 

 posed, as the name implies, of soft-bodied, or gelatinous 

 animals, without either an internal skeleton, or articulated 

 appendages. They are either terrestrial (Geophila), flu- 

 viatile (Limnophila), or marine (Thalasiophila). Their 

 respiration is either aerial (pulmonary), or aquatic (bran- 

 chial). Some aquatic species are air-breathers, and 

 may be termed amphibious. They are either naked, or 

 testaceous ; the latter being either univalve, or bivalve. 

 They are either unisexual, or hermaphrodite. 



Mollusks are, generally, more or less inclosed in a 

 thick, dense skin (the mantle), which varies greatly in 

 form and extent, in different species. It gives attach- 

 ment to a highly complex muscular system of great 

 irritability ; which, when excited, pours out a copious 

 secretion of mucus. In the testaceous, or shell-bearing 

 species, the appropriate parts of the mantle secrete the 

 matter which constitutes the shell, in all its variety of 

 form and color. 



The description, and classification, of those shells, so 



wonderfully varied in form, so exquisitely sculptured, 



so richly painted, ONCE CONSTITUTED CONCHOLOGY. It 



does not do so now. In the zoological, as in the 



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