The Neritas are very abundant in tropical and semi-tropical countries where they live on rocks and stones near low water mark. They are said to be nocturnal and spend the night feeding on seaweed. The shell of the Nerita is solid and heavy and variously ornamented with ribs, pustules and color patterns. The “bleeding tooth shell” (Nerita peloronta), so named from the presence of a red spot near one of the columella teeth, is a typical member of this genus. A species living in the Philippine Islands is said to climb trees to a considerable height. The family Cerithiidae comprises some very handsome shells which inhabit salt, brackish and fresh water. They are found throughout the world but the finest species live in the tropics. The spire is very long and is composed of many whorls. Some shells are smooth and polished, while others are marked by frills, knobs, spines and ribs. The name Cerithium is from the Greek word ceration, meaning a small horn, and is used because of the horn-like shape of the shell. This family has its giants and also its pygmies, the latter being pretty, reticulated shells from one fourth to three fourths of an inch in length, living among the eel grass and other vegetation along the shore. There are over a hundred species of these small shells, and some when handled discharge a bright green fluid. Whoever visits the seashore is bound to become intimately acquainted with the Littorinas, or periwinkles, for they cover the rocky shores everywhere, millions of their rounded shells clinging to the rocks when the tide goes out. They feed on the algae which grows on the shore. They are found in both brackish and fresh water. The common periwinkle (Littorina littorea) is extremely abundant on the shores of southern Europe and the northern part of the United States. In England it is used as an article of food and it is said that nearly two thousand tons are gathered annually and that a thousand persons are employed in capturing it. In London and other large cities they are sold on the street, the animal being picked out with a pin. It is used for bait in some of the fisheries and the oystermen plant many bushels on their oyster beds yearly to keep the seaweeds from accumulating. From these facts it will appear that this periwinkle is of considerable economic importance. All of the species are amphibious, living for a long time out of the water.