The Window Shells - Family Placunidae

THE WINDOW SHELLS - FAMILY PLACUNIDAE. Genus PLACUNA, Sol.

Shell

bivalve, pearly, of flattened, round, laminated, radi ately striated valves; hinge ligament exterior at beaks, running inward in two divergent grooves. No byssus; 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 Window 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 lamina that compose them.

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