Ligament is the membranous or tendinous substance by which the valves or parts of the shell are attached. Some multivalve shells are connected by the parts of one valve locking into another. Plate [I]. fig. 2, D D D. The ligaments vary considerably in their texture, being scaly, prickly, smooth, or punctated.
Ridges are certain convexities in many of the Lepas tribe, sometimes longitudinal and sometimes transverse. Plate [I]. fig. 1, F F.
Peduncle. A sort of stem by which the shells of the Anatifera are attached to wood, &c. It is a membranaceous substance, similar to a bladder but materially thinner, and filled with a liquid which evidently affords nourishment to the animal. Plate [I]. fig. 2, C C; the peduncle is usually affixed to a piece of wood as represented at G.
Feelers are those crenated arms, evolved from the side of the Anatifera. While the animal is in the water it continually moves its feelers, evidently for the purpose of entangling minute marine insects, as food. Plate [I]. fig. 2, E E.
Accessory valves are small plates which cover the apex at the hinge of the Pholades, or are situated below the hinge. Plate [I]. fig. 3, a.
Margin. A fleshy border in which the valves are attached in the genus Chiton. Plate [I]. fig. 11, b b.
BIVALVE.
Bivalve shells consist of two parts or valves, connected by a cartilage, and a hinge which is generally composed of teeth; those of the one valve locking into a cavity in the other.
The valves of some bivalve shells are formed exactly alike, and others are very different; the one being smooth, the other rugose; one flat and another convex; and often one is shorter than the other.
The shells of the Mya, Solen, Tellina, Venus, and others, have in general both valves alike, while those of the Spondylus, Ostrea, and Anomia, have in general dissimilar valves. The first of these kinds are called equivalve, and the latter inequivalve.