“By this,” says Parkinson, “we are taught that innumerable beings have lived, of which not one of the same kind does any longer exist—that immense beds composed of the spoils of these animals, extending for many miles under ground, are met with in many parts of the globe—that enormous chains of mountains, which seem to load the surface of the earth, are vast monuments, in which these remains of former ages are entombed—that, though lying thus crushed together, in a rude and confused mass, they are hourly suffering those changes, by which, after thousands of years, they become the chief constituent parts of gems, the limestone which forms the humble cottage of the peasant, or the marble which adorns the splendid palace of the prince.” Fossil, wood, coral, and shells, are, indeed, as Bergman very forcibly observes, the only true remaining “medals of Creation.” EXPLANATION OF THE PARTS OF SHELLS. MULTIVALVE. A MULTIVALVE shell is composed of more parts than two. Every part of a shell which is connected by a cartilage, ligament, hinge, or tooth, is called a valve of such shell; thus, the Chitons have eight transverse, broad, but very short valves, placed on the back of the animal, and inserted at their sides into a marginal tough ligament. Plate I. fig. 11, _a a a_. _Operculum_ consists of four small valves on the summit of the Lepas, which shut up the superior orifice; it is in a certain degree stationary, and different from the operculum of univalve shells, which will hereafter be described. Plate I. fig. 1, A. Fig. 9 represents a profile view of the operculum removed from its place, _a_ the front valves, _b_ the back valves. Fig. 10 a front view of the operculum. _Base_ is that part of the shell by which it is fixed to rocks and other bodies. Plate I. fig. 1 and 2, B B B.—H is a piece of stone to which the base is fixed, and G a piece of wood to which the shells of this section are generally attached. _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.