CHAPTER XXXIV: THE WINDOW SHELLS 

 Family PLAcuNiOit 

 Genus PL.ACUNA, Sol. 



Shell bivalve, pearly, of flattened, round, laminated, radi- 

 ately striated valves; hinge ligament exterior at beaks, running 

 inward in two divergent grooves. Nobyssus; muscle scar double, 

 large. Animal very much like Anomia. Four species in China 

 and Australia. 



The Saddle Oyster {P. sella, Lam.) begins life with flat, 

 round, transparent valves, but as it grows the margin becomes 

 more wavy, attaining when adult a curvature that imitates the 

 arch of a saddle. The added laminae take on a purplish colour 

 which reflects, inside and out, a pinkish pearly lustre. Half- 

 grown shells are beautifully mottled and semi-transparent. 

 Length, 6 inches. 



Habitat. — Coasts of China and India. 



The Chinese W^indow Shell (P. placenta, Linn.) has flat, 

 circular valves, lying so close as to crowd the animal if it is much 

 thicker than a sheet of paper. They are translucent, faintly 

 rosy-rayed when young, with a yellowish lustrous surface and 

 a gentle curvature of the ventral margin when full grown. 



The laminated structure of these shells permits of their sep- 

 aration into thin sheets, as in the mineral mica. The Chinese 

 have long used these sheets in lieu of glass for window panes. 

 Specimens of the young shells may be obtained in curio stores. 

 Soaking loosens the thin laminae that compose them. 



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