CONCHIFERA OR BIVALVES. 



115 



ligament internal ; 

 no distinct opening 

 for the byssus. Ani- 

 mal unknown. — 7 

 species, recent. 



This shell, which 

 is thin and fragile, lodges in sponges, &c. It 

 is brought from India and Australia. The bys- 

 sus has not been seen, and therefore it is not 

 positively ascertained whether it possesses one. 



73. Pern A. — Shell nearly equi valve and 

 flat, irregular, gaping 

 for the passage of the 

 byssus; bosses small; 

 margins very brittle ; 

 hinge straight and 

 broad, divided into 

 parallel grooves. Ani- 

 mal, foot very small. 

 — 10 species recent, 6 fossil. 



From India, the Cape de Verde Islands, &c, 

 generally found moored to rocks deep in the 

 sea, and occasionally to mangrove trees. Con- 

 siderable clusters are frequently found attached 

 firmly to each other by the byssus. 



I 2 



