Page:Natural History, Mollusca.djvu/297

 extremities are so different from the forms of all other shells, that even the unscientific observer regards them with curiosity and interest. The resemblance which the valves bear to the handle (scales) of a razor is obvious, especially in such species as are slightly curved. The valves are thin and brittle, covered with an olive epidermis which readily peels off. Beneath this the surface is marked with striæ recording the progress of growth, which, following courses parallel to all of the margins, impart a singular and peculiar aspect to these shells.

The animals have the mantle united for a portion of its edges, but allowing the protrusion of an enormous foot, which is thick, long, and somewhat club-shaped at the extremity. The siphons are short, united more or less completely, and fringed at the tips.

The species of this genus, which are not numerous, live in sandy beaches near the verge of low-water, or buried in the soil at greater depths. They are most powerful and skilful burrowers, often lying buried in a vertical position two feet deep, though their ordinary habit is to go only so low in the sand or mud, as to allow the extremities of the siphons just to reach the top. "They may be said to have regular burrows. When the animal is undisturbed, and the tide is in, it lies with the tubes at the entrance of its perpendicular hole. If it be disturbed, down it goes. In short, its life is spent in descending to the depths of its burrow, and ascending from it again, by means of the extension and contraction of its great muscular foot, which is situated at that part of the shell which is lowest."