PULMONAEY GASTEROPODS. 



419 



which last is a numerous family, being found in every sea. All these 

 shells, as their name indicates, represent a winding pyramid, ter- 

 minating in a sharp point, some of them having fluted spirals, others 

 rounded, angular, or flat, and some of them elegantly pencilled. 

 Figs. 239 to 243 represent some of the varied forms they assume. 



The twelfth family, Melaniadse, types, Paludomus and Melania, 

 fresh-water genera. 



The thirteenth family, Cerithiadae, types, Aporrhais and Ceri- 

 tliium. 



Cerithium is a marine shell, which is found in muddy bottoms, on 



Fig 244. Cerithium 

 fasciatum (Brug.). 



Fig. 245. Cerithium 

 aluco. 



Fig. 246. Cerithium giganteum 

 (Lamarck). 



ships, and more frequently at the mouths of rivers, but rarely beyond 

 the point to which the tide reaches. The genus is numerous in 



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