America; Panopaæ, now principally extinct; Thetis, Neæra, Corbula, and Mya, or Gaper. Our fifth family, Solenidæ, contains the Solens, which under the name of "razor-fish" are so abundant on the sandy shores of all parts of the globe. These molluscs live buried vertically in the sand, a short distance from the shore; the hole which they have hollowed, and which they never quit, sometimes attains as much as two yards in depth; by means of their foot, which is large, conical, swollen in the middle, and pointed at its extremity, they raise themselves with great agility to the entrance of their hole. They bury themselves rapidly, and disappear on the slightest approach of danger. When the sea retires, the presence of the Solen is indicated by a small orifice in the sand, whence escape at intervals bubbles of air. In order to attract them to the surface, the fishermen throw into the hole a pinch of salt; immediately the sand becomes stirred, and the animal presents itself just above the point of its shell. It must be seized at once, for it disappears again very quickly, and no renewed efforts will bring it to the surface a second time. Its retreat is commonly cut short by a knife being passed below it; for it burrows into the ground with such velocity that it is difficult to capture it with the hands alone. This shell has by some been compared to a knife-handle; by others to a razor, which has become its popular name. It is a thin, transparent, long, and slender equivalved bivalve, with parallel edges, gaping and truncated at both extremities. The tints are rose-coloured, bluish-grey, and violet; the valves slightly covered with an epidermis of a greenish brown. The animal which lives in this elegant dwelling has the form of an elongated cylinder. Its mantle is closed in its whole length, and only open at the ends at one side for the passage of the food, and at the other for the passage of a tube formed of two syphons united together. This curious shell, various species of which are represented in PL. XIX., are known as razor-fish, sabre-fish, and other names, which in some respects indicate the peculiar form of the shell, as well as its sharpness. [Illustration: PLATE XIX.--Razor-fish. Solenidæ. I. Solen siliqua. (Linn.) II. Solen vagina. (Linn.) III. Solen ensis. (Linn.) IV. Solen ensis major. (Lamarck.) V. Solen ambiguus. (Lamarck.) VI. Solen legumen. ] The Tellinidæ, the sixth family in our table, is very important, as including a vast number of genera and species, of which, as types, we will particularise Tellina and Donax; but Galatea, Mesodesma, Semele, Sanguinolaria, Psammobia, and Capsula, are important genera.