Page:Popular Science Monthly Volume 50.djvu/62

50 The Noah's ark is a most oddly shaped shell, and was named by Linnæus from its resemblance to that primitive craft. One ark found in the Mediterranean sometimes contains violet-colored pearls, and one on our coasts is called the "bloody clam," from its fiery gills and the crimson fluid in its tissues. Some of the arks live in submerged clefts of the rocks, and are so busy eating and growing that before they know it they have grown too large to get out, and must remain prisoners for the rest of their lives.

The teredo, or ship worm, would hardly seem to belong with this group of animals, but it is a true bivalve, having a pair of tiny shells at one end of its wormlike body. It has been a most terrible pest ever since men began to traverse the ocean, for its favorite home is the bottom of a wooden ship. It belongs to a family of borers. Some bore in coral, some in rock, and others in wood. The baby teredo, when floating about in the water, comes across a vessel or piece of wood, and immediately begins to bore into it with the edges of a pair of pallets which it has for the purpose. As it proceeds, a calcareous lining is formed to the burrow, which increases in size as the teredo grows. It never leaves its hole again during life.

One very curious fact connected with the teredo is that the burrow of one never runs into nor crosses the burrow of another, even though the wood between is no thicker than a sheet of paper. These little fellows work very rapidly, as the following item from Quatrefages will show: A ship was sunk near St. Sebastian, Spain, and in four months, when it was raised, all thetimbers and planks were so riddled with teredo burrows that they were entirely worthless.

The most brilliant and withal attractive shells in my collection are from the West Indies. I call them sunset shells, because they look as the sky often does on a beautiful summer evening. They are somewhat like clam shells in shape, but narrower and flatter, and most delicately finished. Some are flushed with delicate pink, with rays of pale yellow, others are violet and white, still others green. All the colors of the rainbow are here blended and harmonized with the matchless perfection with which the Great Artist works.

The univalves are more highly developed than the bivalves. They are called Gasteropods, which means stomach-footed,