COXCHIFERA. 269 



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



Fig. 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 



Fr.,. 206.— PHoi.ADKS. 

 * (pw\evco, plioleuo, to lie in a hole. 



