192 BIVALVES. 



Many and great are the dangers attendant on 

 this employment. The greedy shark often 

 marks the diver for his prey, his only chance of 

 safety under such circumstances, is by muddy- 

 ing the water, and so eluding the animal's obser- 

 vation. A large flat fish also sometimes attacks 

 him, and keeps him under water till he is drowned. 

 When drawn up in safety to his vessel, he often 

 in consequence of his exertion discharges blood 

 from his mouth and nostrils. The divers rest 

 and labour alternately, during periods of about 

 ten minutes. 



Genus PINNA (Plural, Pinna.) 



Generic Character. Shell bivalve, equivalve, 

 fragile, thin, gaping at one end, and furnished 

 with a byssus ; shape subtriangular, narrow at 

 the beaks, and expanding to a considerable 

 breadth at the opposite extremity ; hinge with- 

 out teeth ; valves united by a long external 

 ligament. 



* Plate X. figure 3. 



