"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.
PHOLAS.
"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.
PHOLAS.
"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.