MOLLUSCA. 183 



latter is the most important, I shall speak of 

 it first. 



On the shores of those countries where pearl 

 oysters abound, they are sought for as eagerly as 

 we seek for Ostrea edulis on our coasts. We have 

 seen how the latter is at present drawing the 

 attention of practical men, who are endeavouring to 

 perfect its breed, and to propagate its species 

 widely. Such will doubtless happen one day for 

 the pearl oyster, whose products are so valuable ; 

 for not only does this mollusc produce the pearl 



FIG. 22. Avicula margaritifera (Pearl-oyster) , 



the "jewel of the sea," but also that beautiful 

 substance known as mother-of-pearl, with which 

 buttons, knife-handles, penholders, work-boxes, and 

 ornaments of every description, are constantly manu- 

 factured. 



The animal in question is the Avicula margariti- 

 fera, L. (Fig. 22). Its shell, of a semicircular 



