The Wing Shells, Pearl Oysters and Hammer Oysters 



The Pod Perna (P. legumen, Rve.) is a small quadrangular 

 white shell, three times as long as it is wide. 



The Carpenters' Square (P. isognoniim, Rve.) is a well 

 known representative of this genus. The elongation of the body 

 of the shell seems to shorten the wing, and vice versa. The angle 

 formed is close to ninety degrees. Colour, dark purple. Length, 

 6 to lo inches. 



Habitat. — Philippines. 



The Bat Perna (P. vespertilio, Rve.) strikingly imitates 

 the shape of a bat's wing. It is yellowish white, tinged witli 

 purple. Length, 6 to 8 inches., 



Habitat. — Bay of Manila. 



THE HAMMER OYSTERS 

 Genus MALLEUS, Lam. 



Shell nearly equivalve, elongated, irregular; dorsal margin 

 prolonged almost at right angles with the valves. A small genus 

 distributed in Chinese and Australian seas. 



The Common Hammer Oyster (A/, vulgaris, Linn.) is the 

 type, and Lamarck could not but call the genus Malleus, for 

 there was the handle and head of this familiar tool closely imi- 

 tated by the valves and elongated wings of the new and unknown 

 mollusk. The coarse, thick valves are drab or black and undu- 

 lated. They frequently slant obliquely from the hinge line, 

 and curve decidedly. In early life the shell is like those of Avicula 

 and the byssal cord passes out through a deep sinus in the right 

 valve. Later the extension of the valve in three directions gives 

 it the characteristic form, and the byssal sinus is midway between 

 the two valves, causing an indentation of each. The lining shows 

 that the body lies in a roundish space near the hinge, attached 

 by a large muscle scar. Length, 6 to 8 inches. Width, 8 to lo 

 inches. 



Habitat. — China Seas. 



The White Hammer Oyster (A/, alius, Rve.) diflFers from 

 the preceding species by being colourless, and of fmer and more 

 horny texture, and less rude pattern throughout. Length and 

 width, 6 to lo inches. 



Habitat. — Philippines. 



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