Inferior Ear. Do. do. i.
Margin. The extreme edge of the whole shell, or the circumference of either valve, all round. Plate [I]. fig. 4, p; and Plate [II]. fig. 1, p.
Crenulated margin. That fine notched edge of shells, which unite into notches in the opposite valve, as genus Donax. Plate [IV]. fig. 6, m m.
Striæ are fine thread-like lines, generally on the exterior surface of shells, and are sometimes both longitudinal and transverse. When the striæ of shells appear indistinct, as if worn out, it is termed obsolete striæ. In some instances the insides of shells are striated; for example, the Fasciolaria Tulipa. The character of the striæ is often of much use in distinguishing species. Plate [II]. fig 2, f.
Right Valve is that valve which, when viewed with the inside uppermost, has the anterior slope pointing to the right hand. Plate [I]. fig. 8; and Plate [IV]. figs. 5 and 6, B.
Left Valve. The opposite of the above; the anterior slope points to the left hand, when viewed from the inside. Plate [IV]. figs. 3, 6, 7, 9, &c.
Length of the Shell is taken from the ligament, or the beak, to the opposite margin. For example, Mytilus: it is longer than it is broad, and the Solens are broader than long. Plate [I]. fig. 5, u u; and Plate [II]. fig. 4, v v.
Breadth is measured from the most extreme edge of the anterior and posterior slopes, being in a contrary direction from its length. Many shells are broader than long, such as most of the Myæ, Solenæ, Tellinæ, &c.; and the Mytilus, Ostrea, Pinna, &c., are in general longer than broad. Plate [I]. fig. 5, v v. Plate [II]. fig. 4, v v.
Byssus, or beard, is an appendage composed of filaments of a silky texture, by which some of the Bivalves fasten themselves to their beds, such as the Mytilus, Pinnæ, &c. Plate [II]. fig. 6, s.