Page:Natural History, Mollusca.djvu/281

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mary ones called cardinal are oblique, and one
lateral remote on each side. The valves are almost always covered with well marked ribs alternating with furrows, which radiate from the beaks to the margins. These ribs are sometimes studded with spinous scales. The ligament is external and conspicuous though short.

The animal is shaped much like the shell, being round and swollen, with the mantle open in front, the edges of which are usually plain, but strongly fringed in the neighbourhood of the two siphons; the latter are short, slightly separated and fringed around the edge. The foot is very large, cylindrical, with a conical tip directed forwards. It is bent, with an