Page:Natural History, Mollusca.djvu/268

256 the faculty of spinning is confined to the early life of the animal, but in others a strong and copious byssus is formed at pleasure through life.

The name of this familiar shell-fish is derived from the obvious resemblance which its shell bears to a mouse, the united beaks representing the nose. The Greeks used the term Mύς for both the shell and the quadruped, and both the Latin term Mytilus and our own Mussel are derived from that appellation.

The genus is characterised by a shell very unequal-sided, but equal-valved, somewhat triangular, running off into pointed terminal beaks, the valves swelling, the surface covered with a horny skin; the hinge, though sometimes notched, has no true teeth; the narrow ligament is internal.

The animal is lengthened and oval, the lobes of the mantle are simple or fringed, united behind in a single point, so as to form an anal siphon. The mouth is rather large, furnished with two pairs of soft lips. The foot is slender, strap-shaped, grooved, carrying at its base a silky byssus of considerable strength.

The Edible Mussel (Mytilus edulis) is the only British species, but is too abundant and too well known to need description. Sold in every town as an article of food, its three-sided shells, black without and blue within, and the bearded animal, both in its raw and cooked state, are familiar to every one.

Dr. Knapp of Edinburgh has communicated to Messrs. Forbes and Hanley a very interesting