286 



the animal having then made the final deposit of tes- 

 taceous matter, has completed the colored pattern or 

 design, and covered it with a beautiful transparent 

 enamel. 



The animal possesses two membranous -extensions 

 on that part of its body called the Mantle by ana- 

 tomists, in the form of wiugs, which furnish the tes- 

 taceous and coloring matter; these increase in size, 

 as the shell advances in growth, and when it has at- 

 tained its maturity, fold over, and totally conceal the 

 whole of it, during the animal's removal from one spot 

 to another, or from the necessity it is under of partially 

 quitting its habitation in search of food. 



In some species these membranous wings do not 

 quite meet on the convex part or back of the shell, and 

 the space that separates them, with the unequal termi- 

 nation of their edges, is invariably marked by a dis- 

 tinctly colored dorsal line, which is strongly defined 

 in the C. mappa. In general, these wings are long 

 enough to overlap each other, and the pattern and co- 

 lors are then more equally distributed over the whole 

 surface of the shell. The circumstance of frequently 



