MOLLUSC A. 



of classidcation. It is very common to find the halves 

 of bivalve shells with a neat little round hole in 

 them. This hole is the work of the odontophore of 

 some carnivorous gasteropod. It will usually be found 

 not far from the hinge, or in the neighbourhood of 

 the adductor muscle of the bivalve; the shell opens 

 wide when this is cut, leaving its tenant an easy prey. 



Fig. 75. — Examples of Holostoniatous Gasteroporis. 1, The Wimble Shell, 

 Turriteila terebra; 2, A Wentle-trap, Scalaria similis; 3, The Biver Snail, 

 Paludini vivijpara ; 4, Its operculum, with concentric mai-Kiiigs ; 5, One hori- 

 z jntal row of teeth from its odontophore, magnified. 



The shell of a gasteropod is usually spiral, but in a 

 few cases it is flat, as in the common Limpet, or nearly 

 so, as in the Sea Bar. 



It is usually considered that the carnivorous species 

 of the Gaxteropoda may be known by a notch at the 

 back of the shell; and according to the presence or 

 absence of this notch, the Gasieropodahaye been classi-^ 



