CONCHOLOGIA CESTRICA. 

THE MOLLUSCA. 
HE 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 (Geophz/a), flu- 
viatile (Lzmnophila), or marine (Thalasiophila), Their 
respiration is either aerial (pu/monary), or aquatic (dran- 
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 (¢he 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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