SAXICAVA. 



The species of this Genus are not numerous, they 

 are not, however, easy to distinguish from each other. 

 They are frequently found upon the outside of oysters 

 protected by their irregularities, and in clefts of rocks or 

 corals, roots of sea weeds, and even perforating oysters, 

 chalk, limestone, and hardened clay ; those which them- 

 selves perforate the hollows, in which they live, are more 

 regular than the others. , 



We have drawn at 



Fig. 1 . Saxicava nigosa, young shell. 



2. inside, showing the teeth, 



3. A full grown specimen of the same. 



4. The inside, showing the muscular impressions. 



