Chiton squamosus.
“Although,” says Lamarck, “when we examine this creature, and observe the several pieces of which its shell is composed, attached to the marginal membrane of the mantle which surrounds them, it appears not a univalve, but a multivalve shell; yet these shelly pieces ought not to be regarded in any other light than as a lengthened shell of one piece, which Nature had originally broken transversely into several distinct moveable pieces, to give greater freedom to the animal in its movements.”
The Chitons, like the neighbouring genera, frequent the rocks between high and low water mark, but are much more active in their movements. Poli, a learned Neapolitan, in describing the anatomy of a Chiton, says, that the interior of the mouth or throat of this animal is covered with a multitude of teeth,—some simple, and others with three points, and that these teeth are disposed in numerous longitudinal rows.
CLASS CONCHIFERA.
The Conchifera differ from the Molluscous animals that bear shells, in a very great degree; for, although the substance of the body is soft, unlike the Mollusca it is inarticulate, always enclosed in a shell of two valves, without head or eyes,—a mouth, if it may be so called, concealed from view, and without any hard parts, and the whole body enveloped in a large mantle, or hood, formed of two thin lobes, generally perfectly free, but at times united in front; these are the principal distinguishing characters of this class.
In earlier systems, when shells were classed without much reference to the animals that inhabited them, the only distinction made was the number of pieces of which the shell was formed, and they were arranged under the heads of univalves, of one piece, bivalves, with two pieces, and multivalves, with more than two pieces. This arrangement was inconvenient, as, in some cases, it separated animals that otherwise agreed with each other. With respect to the bivalve shells, however, this objection does not hold good, as they all contain animals belonging to the class Conchifera.
The individuals of this class appear to be deprived of all the senses except that of feeling. Their powers of motion have been so well described by Dr. Roget, in his Bridgewater Treatise, that we cannot do better than extract a portion from that interesting work.