class="fig_caption">

"To begin with the first division, Multivalves. There is a group of Lepades, it is the species called goose-barnacle, of which so many strange and silly tales have been told in former times. (Plate 2, Lepas anatifera.) This species is furnished with a kind of stem, like a bladder, and is called the peduncle, (c) and is fastened to other bodies. The feelers (d) are feathery projections, which the animal keeps in continual motion, for the purpose of catching its food. Here is a group of another kind; (Plate 2, Lepas tintinnabulum;) these are without a peduncle, and are called sessile. The base (a) is that part of the shell by which it is fixed to other bodies: (a) the operculum is formed of four small valves on the summit. (b).

"In the shells of the second division, Bivalves, we shall find a greater number of parts. Valves are the different pieces that compose a shell. When both the valves are alike in form, the shell is called equivalve: when the valves are different in the same shell, it is called inequivalve. Mya, Solen, Tellina, are equivalves: Ostrea, Anomia, Pinna, &c. are inequivalves.

"The hinge is formed by the teeth of one valve inserting themselves between those of the other valve, in some genera; in others, by the teeth fitting into the cavities of the other valve (Plate 3., a.) When the teeth are placed in the centre of the hinge they are called cardinal teeth. Lateral teeth are situated on the sides of the valves, and are generally long and flat, sometimes hollow. Some hinges are straight, others curved. Here is the hinge of Arca, furnished with many small teeth. (Plate 3, b.)

"The ligament is a membrane that connects the valves, and keeps the hinge in its proper place: it is always situated near the beaks. The ligament is very perceptible in the cockle, in Pecten, or scallop, in Tellina, &c.

"The beaks are the most pointed parts of the bivalve shell (Plate 3, c.); when the valves are closed, the line where they meet is called the seam. (Plate 3, d.)

"The anterior slope is that part of the shell where the ligament is placed, and is also called the area. (Plate 3, e.) The posterior slope, or areola, is the other side of the beaks. (f.)

"The lunula is a crescent-like depression on either the area or areola. The edge of the valve is called the margin; it is often finely crenulated, or toothed. The interior of the valve is called the cavity. (g.) In the valves of this ark-shell here are two broad marks, shining and glossy. (g.) In those of the oyster and muscle that I now show you, there is but one. These marks are muscular impressions; they are the parts where the muscles of the animal have been affixed, and are termed cicatrix.

"Ears are two processes on each side of the beak; the Pecten, or scallop, is an example. (Plate 3, i.)

"Sinus, in bivalve shells, is a small hollow in the hinge.

"Byssus, or beard, is an appendage composed of silky threads, by which the muscle and Pinna fasten themselves to the rocks. (Plate 3, f.)

"Cordiform is a term applied to heart-shaped shells.

"A cartilage is the same as a ligament. When the valves of a shell are very nearly flat, they are said to be compressed: when a valve has teeth, it is said to be dentated.

"When the valves of a shell do not shut close, they are said to be gaping. (Plate 4, Mya.)

"A muscle is a fleshy, pliant organ, by which the animal is attached to its shell. I have already pointed out to you the impressions of those muscles within bivalve shells.

"A suture is a toothed joint, in bivalves.

"A shell with ears is said to be auricled.

"The third division, Univalve shells, have also their several parts. The first section has a regular spire. Here are two shells of this section, Voluta and Buccinum, both sawed asunder, in order to show the interior structure of the shell. (Plate 3.) The aperture, or opening, being turned towards you, the front of a univalve is seen; reverse it, and you see the back.

"The top, or highest part, is the apex; (a) the lowest part is the base of the shell. (b.)

"The spire (c) is formed of wreaths, or whorls, (ddd) which terminate in the apex: the lowest whorl is the body of the shell. (e.)

"The aperture, opening or mouth, (f) as it is sometimes called, is on the right-hand when the front of the shell is turned towards you. The aperture is an important distinction in