262 



CONCH1FERA. 



The Pearl-Oysters are obtained by diving in about 

 twelve fathoms. Many lives are annually sacrificed 

 in pursuit of these highly-prized baubles. 



The second family of Conchiferous Mollusks com- 

 prehends 



The Mussels (Mytilacea), all of which are furnished 

 with a foot, enabling them to creep about, and by 

 its assistance they construct a cable composed of 

 horny threads, called Byssus, whereby they attach 

 themselves to rocks. 



FlG. 198. ANIMAL OF MUSSKL. 



The Wing-Shells (Pinna) are remarkable for the 

 fineness of their byssus. When mingled with about a 

 third of real silk it is sometimes spun, and manu- 

 factured into gloves, &c., but they are merely objects 

 of curiosity. 



