. Cuvier's animal kingdom : arranged according to its organization. Animals. 362 MOLLUSCA. duce the water to the branchial cavity placed upon the back, and closed in every other place. The respiratory organ consists in a few small leaflets, attached in a transverse line to the bottom of that cavity. The animal appears to have no tentacula, but only a narrow veil upon the head. There are species in wluch the shell shows no appearance of the groove, and would perfectly resemble a Patella were it not that its vertex is turned backwards. [We must observe, says Rang, that we have seen young Patellœ
. Cuvier's animal kingdom : arranged according to its organization. Animals. 362 MOLLUSCA. duce the water to the branchial cavity placed upon the back, and closed in every other place. The respiratory organ consists in a few small leaflets, attached in a transverse line to the bottom of that cavity. The animal appears to have no tentacula, but only a narrow veil upon the head. There are species in wluch the shell shows no appearance of the groove, and would perfectly resemble a Patella were it not that its vertex is turned backwards. [We must observe, says Rang, that we have seen young Patellœ to have the character of Siphonaria, and to preserve traces of it at a more advanced age: it is only then provisionally that we adopt this genus, and assign it a place among the Inferohranchiata.'] SiGARETus, Adans. The shell is flattened, with an ample round aperture, and an inconsiderable spire, whose whorls enlarge very rapidly, and are visible on the inside. It is hidden during life in the fungous shield of the animal, which projects considerably beyond it, as well as the foot, and is the true mantle. We observe in front of this mantle an emargination and a semi-canal, the use of which is to conduct water into the branchial cavity, but which leave no impressions on the shell. The structure indicates a transition to the following family. The tentacula are conical, with the eyes at their exterior base : the penis of the male is very large. There are species on our own coasts. [This remark is erroneous, unless we consider Cuvier's Sigaretus the same as Pleurobranchus. See some remarks on the confusion in the nomenclature of this genus by Mr. Gray, in the Zool. Jouni. i. p. 428.] Cariocella, Blainv., is a Sigaretus with a horny and almost membranous shell, like that of Aplysia. The Cryptostoma, Blainv.— lias a shell very similar to Sigaretus, supported, with the head and abdomen (which it covers), on a foot four times its size, cut square behind, and which produces in front
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