Among the myriads of shells which we may select to illustrate the various interesting types, shapes, and kinds, are the Chitons (Fig. 101). Their shells are made up of many plates resembling the plates of a hawkbill turtle. Many live in holes in the rocks, and all have a very large, sucking, disklike foot which clings to the rocks with great tenacity. Resembling them somewhat are the limpets. These are interesting and beautiful shells, especially when polished, forming attractive domes marvelously tinted and colored. Some are called keyhole limpets (Fig. 102), from the fact that they have a keyhole-like opening in the top. They range in size from very minute forms to giants a foot in length. [Illustration: FIG. 101.--The Chiton and its free-swimming young. I. Adult, showing plates. II. Chiton dissected: _o_, mouth; _g_, nervous ring; _ao_, great artery from the heart, aorta; _c_, ventricle; _c´_, an auricle; _br_, left branchiæ; _od_, oviducts. III, IV, V. Development of free-swimming young.] Among the most beautiful of all shells, and at the same time the most common in tropic and semitropic seas, are the abalones. They are also called ear shells. They have an enormous foot that covers the entire lower surface, being a remarkably powerful organ. Instances have been known where Chinese abalone hunters have tried to pry off the shell from a rock with their hands, and have had their fingers caught and held as though by a vice. [Illustration: FIG. 102.--Keyhole limpet.] The Haliotis is very common on the shores of the southern Californian islands. In some localities every rock is covered with them, and in places where the black abalone is common, I have found them piled one upon the other. There are two hundred species living. Every tint, color, or tone known in the scale of color, or its combinations, is flashed from these marvelous shells, which, if rare, would be counted among the most beautiful of all natural productions. On the Californian coast they are collected in large numbers, and when polished are converted into buttons and a thousand and one other objects. The meat, which is of excellent quality, is sold in large quantities to the Chinese. Thousands of the shells are bought by tourists, the outside being richly polished. From the ancient graves or Indian mounds of the Californian islands I have taken quantities, especially the large kind known as the red abalone, showing that they were used by the ancient inhabitants. In all of these islands heaps and piles of abalones are found far from the water. By stopping up the holes in the shell with asphaltum, which drifts ashore here, the natives had an excellent dish, or bailer. They cut the shell into earrings and ornaments of many kinds, and most of their fishhooks were evolved from this beautiful shell, which also supplied a large proportion of their food. [Illustration: FIG. 103.--Great conch (_Strombus_).] [Illustration: FIG. 104.--Queen conch (_Cassis_).]