322 



POPULAR CONCHOLOGY. 



nearly transparent. Animal very little known. — 3 or 4 

 species. 



Found on sand in the Indian, Chinese, and Red Seas. 

 The Placuna Placentia, commonly known as the Chinese 

 window oyster, is sufficiently transparent to be used for 

 windows and lanterns, as horn is used in this country.* 

 Though the animal has not been much examined by 

 naturalists, it is obvious that it must be exceedingly flat ; 

 indeed, not much thicker than a shilling ; for the valves, 

 when closed, appear nearly to touch. The shells are 

 sometimes waved, and bent in a curious manner. 



Placunanomia. Brod. — Shell irregular, nearly equi- 

 valve, smooth, plaited round the 

 edge, and somewhat glossy in- 

 side ; the hinge consists of two 

 narrow ribs, unequal in length, 

 and converging at the base, in 



one valve, and in the other 

 two corresponding grooves ; the 

 lower valve has a longitudinal 

 hole near the hinge, and the 

 opening is entirely filled up by 

 the ossification of the tendon 

 passing through it; besides the 



muscular impression in the upper valve, there is a mark 

 which shows the attachment of the other extremity of the 

 tendon of adhesion. Animal unknown. — 10 species, (Gray). 

 Mr. Cuming found one species of this singular shell 



Placunanomia. 



* Mr. Gray mentions that the Chinese use the powder of this shell 

 as silver in their water-colour drawings. He has himself used it in 

 colouring the figures of fish with good effect. It is hot quite so 

 brilliant as the powdered leaf metal, but it has the advantage of not. 

 changing colour by exposure. 



