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Superior Ear. Plate IV. fig. 11, h.

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.