404 MARGARITACE,E ; MALLEUS ; PERN A ; PINNA. 



pended from the neck to receive them, and they are then drawn 

 up on giving signal to those above. Each diver can repeat 

 this operation about fifty times in one day; but it is not uncom- 

 mon to see, after several descents, blood streaming from the nose 

 and ears. The shells are laid out that the animals may die ; and 

 when this has taken place (which is known by the opening of 

 the shell) the interior is searched for pearls, and the best shells are 

 set by to furnish mother-of-pearl. The produce of this operation 

 is very considerable. 'In 1798, the pearl-fishery of Ceylon 

 yielded the sum of 200,000/. ; but the banks seem to have been 

 too much exhausted, as the produce of the subsequent years 

 was much less, and it has not since risen to the same amount. 



944. The Malleus, or Hammer-oyster, is another genus which 

 is chiefly worth notice on account of its singular form ; the two 

 sides of the hinge being extended so as to resemble in some 

 degree the head of a hammer, whilst the valves, elongated nearly 

 at right angles to these, represent the handle. In the Perna the 

 hinge has no teeth, but several parallel depressions opposite to 

 each other in the two valves, and lodging as many small elastic 

 ligaments. Many fossil species of this character, some of them 

 of great size, exist in the Lias, Oolite, and other more recent 

 strata. 



945. The Pinna, or Wing-shell, approaches the Mussels in 

 many respects. It has two equal wedge-shaped valves, united 

 by a ligament along one of their sides ; and is almost entirely 

 composed of the cellular substance formerly described ( 869). It 

 sometimes attains a considerable size ; measuring as much as 

 three feet in length. The most interesting peculiarity of this 

 genus, is the lyssus, which is remarkably long and silky. The 

 animal fixes itself by this to submarine rocks and other bodies ; 

 and lives in a vertical position, the point of the shell being under- 

 most, and the base or edge above. It even attaches its byssus 

 to a sandy or muddy bottom ; and in such situations large troops 

 of them are found at the depth of a few fathoms. The most 

 common species exist in the Mediterranean ; and the inhabitants 

 of Sicily and Calabria seek them, not merely for eating, but to 

 gather the byssus, of which a stuff may be formed that is 



