The Duck-Bill Shells and Lantern Shells - Family Anatinidae

THE DUCK-BILL SHELLS AND LANTERN SHELLS - FAMILY ANATINIDAE.

Shell

thin, pearly within, granular outside; hinge toothless, pitted; ligament thin, external, with free ossicle; siphons long, united or free; mantle margins united; gills mostly single on each side; foot finger-like; palpi long, narrow.

A family represented as fossils in all the sedimentary rocks and all over the world, though nowhere very numerous. Tryon lists thirty-six genera. Of these over half are quite extinct, and those with living species form but a scant remnant of the family. Its highest development was reached during the Jurassic Period.

Genus ANATINA, Lam.

Shell thin, hyaline, silvery white, smooth, granular toward margins; constriction forms a neck below the posterior, beak like extension which gapes widely to give exit to the united and sheathed siphon tube; hinge has spoon-like process in each valve; hinge ligament elastic.

An Oriental genus of thirty species named from a fanciful resemblance of the valve to a duck's bill.

The Truncated Shell (A. truncata, Lam. ), abruptly squared at the posterior end, rounded in front, flat tened and somewhat incurving on the margin opposite the hinge, is abundant in the Bay of Manila. It is about three inches long.

There is no American species of this genus.