Page:Popular Science Monthly Volume 50.djvu/67

Rh bishop's miter, and are found in the Philippine Islands. If an enemy approaches, their occupants throw out a purple fluid and escape under cover of the stained water.

Notice in the miter shell how the color spots correspond to the whorls, in the scallops how the shades and bands follow the lines of growth. Have you ever thought why this is so? The mantle which builds the shell has spots or bands of color scattered through it, and as it works, the impressions of these same pigment spots are left on the shell. If the pigment cells of the mantle be yellow, red, or violet, these colors will be left on the shell and preserved forever.

Another marvelous accomplishment of the mantle is the ornamentation of shells with prongs, flutings, etc. We have a good example of this in the lovely Murex shells. The mantle sometimes works without cessation until the shell is finished, then turns up, forming the lip (the edge of the aperture). Often it works for a time, turns up, forming a frill or row of points, and rests. Then it begins its labors anew, building an addition and ornamenting it in like manner. Sometimes the mantle turns up at the end in a number of fingerlike radiations, as in the Pterocera lambis and curious pelican's foot.

The cowries form an immense group, some species of which inhabit almost every shore. They are called porcelain shells, on



account of their glossy, smooth texture. The little white cowries are used in some parts of Africa for money and to make girdles for the high chiefs. A stripe of a different shade from the body of the shell runs along the back, showing where the edges of the mantle met. In life it entirely covers the outside of the shell.

The helmet shells of warm seas are used for making exquisite cameos, the best being cut at Rome. The raised figure is