Читать книгу The Conchologist's First Book онлайн

9 страница из 26

Base is the reverse of the above, or that part of the shell immediately opposite the summit. Plate I. fig. 6 and 7, d d.

Sides, the right and left parts of the valves. Plate I. fig. 6, c.

Posterior slope is that part of the shell in which the ligament is situated. In viewing the posterior slope in front, the beaks of the shell retire from view. Plate I. fig. 4, i.

Anterior slope, that part of the shell opposite the posterior slope; in viewing it in front, the beaks point to the observer. Plate I. fig. 4, k.

Disk, the convex centre of a valve, or most prominent part of the valve, suppose it with its inside lying undermost. Plate I. fig. 4, o.

Inside, the concave part of a valve. Plate IV. fig. 6, m.

Muscular impression is the impression left on the inside of the valves, by the adhering muscles of the animal. It differs in most shells, according to the shape of the animal, as semi-ovate, round, lunate, elongated, &c. As a specific distinction, it is often of great use; being, with a very few exceptions, alike in shells of the same species. Some shells have only one cicatrix, as the Edible Oyster and Mytilus; others have two, and some few more; the Tellina for example. Plate I. fig. 6 and 8, e e e e.