CONCHIFERA. 269 



more than six inches deep, so that unless there be a 



Fro. 205. SAXICAVA. 



new surface exposed by the destruction of the per- 

 forated part, there is not much danger to be appre- 

 hended from them. 



The Pholades* are likewise borers. They excavate 



Fir;. 206. PHor.ADi-'S. 



evw> pholeuo, to lie in a liole. 



