Buccinum, whelk, ex. B. reticulatum.

* Strombus, screw, ex. S. pes-pelicàni.

* Murex, rock-shell, ex. M. ramòsus.

* Trochus, top-shell, ex. T. bifaciàtus.

* Turbo, wreath, ex. T. muricàtus.

* Helix, snail, ex. H. nemoràlis.

* Nerìta, nerite, ex. N. striàta.

* Haliòtis, ear-shell, ex. H. tuberculàta.

2nd Section, without a regular spire: 5 genera.

Total number of genera in the arrangement of Linnæus, thirty-six.

The genera marked with an asterisk, contain species found in Britain.

"Multivalves may be divided into two kinds, the pedunculated, or those fixed to other bodies, as rocks, stones, planks, &c.; or free, as the Chiton and Pholas.

"Our first genus is Chiton. The shell is easily known. The fixed character is, many valves placed over each other along the back. I have already noticed the membrane which connects the valves, which is also a permanent character. It is elastic: the sides are either scaly, as in C. squamòsus, (Plate 1,) and hairy, or spinous. The species are determined by the margins. Some of the Chiton genus are common upon our own coasts; they are frequently found among seaweed and stones, rolled up like a ball. C. fasciculàris and C. lævis are British; there are some other British species. The animal adheres to rocks, like the Patella, or limpet. The number of species forty.

"Second genus, Lepas. Shell multivalve, fixed at the base; valves erect, or upright.

"Observe how much the situation of the valves differs in Chiton and Lepas. It is scarcely possible to mistake the one for the other. The feathery tentacula, or feelers, of Lepas anatifera are worthy notice, and in a state of motion must be yet more beautiful. (Plate 2.) The common acorn-shell, L. balanus, is to be seen very frequently upon the shells of muscles, oysters, periwincles, whelks, in large groups. I see that you are examining the different appearance of the pedunculated and the sessile Lepades. Linnæus made two divisions; later writers have separated them into several distinct genera, which will be noticed when we attend to Lamarck's system. The species are forty-five, of which several are found on the British shores, as L. tulipa, L. diadema, L. tintinnabulum, L. balanus, L. anatifera, &c. The Indian, American, and Atlantic oceans afford numerous species.

"Third genus, Pholas. Generic character: shell bivalve, gaping or divaricated, with several smaller hinges situated upon the hinge; hinge recurved, with an incurved tooth."

"Father," said Charles, "I must say that the Pholas shell is very unlike those of the multivalve division: I think it should rank with bivalves."

"So many conchologists have judged; nevertheless it possesses more than two valves, and, according to the system, it must be forced into the division of multivalves.

"The Pholades are found in company, but each individual occupies a distinct habitation, which the animal excavates for itself, either in rocks, in wood, coral, or sponge; but the finest specimens are usually to be seen in chalk. In proportion as the animal increases in size, it enlarges the cavity in which it is stationed. The animal is supposed to effect this operation by means of a corroding fluid that is secreted in the body, and which it has the power of ejecting upon the substance into which it has entered.

"The Pholas has the power of emitting a phosphoric liquor, which shines with brilliancy in the dark.

"I must remind you that the accessory valves are fixed to the margin of the shell by a gelatinous substance; this decays after the death of the animal, and consequently the smaller valves are frequently wanting.

"The number of species is twelve. Several of them are found on our coasts. The Pholas genus is without colour, but the reticulations in some species are exceedingly delicate. Pholas candida (Plate 2) is found on the shores of Kent; you will be pleased with the shells. Pholas dactylus is larger and coarser, and not at all uncommon.

"We have now finished our first division, and must proceed to the bivalves."

CHAPTER IV.

Second Division.—Bivalves: 14 genera.

"I fear," said Charles, "that this new division will be rather difficult, for my father tells me that we must pay particular attention to the hinges of bivalve shells."

"Then apply yourself to the study of hinges, Charles, and your difficulties will chiefly disappear," answered Mr. Elliot.

"The hinge of Mya, the first on the list, is easily known. The generic characters are, shell gaping at one end, hinge mostly with one thick spreading tooth, not inserted into the opposite valve. The Mya race burrow in the sand. Here is Mya arenaria, a large thick shell, frequent on the shores of Kent: the large tooth is sufficiently plain in this species. Mya truncata (Plate 4) is as common, and the curious membranous case, which you will find attached to one end of the shell, is a guide to the species. Both these species are without colour, and have little to attract in their outward appearance. The genus, however, according to Linnæus, varies exceedingly, and contains forty-one species.

"Solen. Shell bivalve, open at both ends, tooth of the hinge subulate, or awl-shaped, reflex, often double.

"In this genus, the great length, in comparison with the breadth of the shells in many of the species, is remarkable: some are exceedingly brittle. Our example, Solen siliqua (Plate 1) is a British species. The hinge is not in the centre of the shell, but nearer to one end of it. Some are shaped like the handle of a knife or a razor, others are bent resembling the blade of a scimitar. The Solen lives in the sands of the sea-shore, often burying itself two feet deep,