30 THE ELEMENTS 



shells, affixed to the animal, some- 

 times of a testaceous, in others a car- 

 tilaginous substance. It is only cal- 

 culated for the protection of the ani- 

 mal, when it retires within its dwelU 

 ing, of which it may be termed its 

 door, and is adapted to the shape of 

 the aperture, which it closes nicely 

 up. Every one must have observed 

 the cartilaginous operculum of the 

 common periwinkle, (the Turbo Litto 

 ratus of Linne,) which has a brown 

 horny appearance, and must in gene- 

 ral be removed, before the animal cai> 

 be taken out when boiled. Plate 3d, 

 ^Si' 4th. 



Vj Spire is all the whorls of the shell, 

 except the lower one, which, as before 

 observed, is termed the body of the 

 shell. Plate 2nd, fig. 12th, i>; and 

 plate od, figures 7th and 8th, Z> J9. 



The spire is a prominent feature of 

 the Univalve ; and upon its being ele- 

 vated, depressed, &c. depends much 



