a. Species with the Mantle-Border, or marginal ligament, eori aceous and naked. Examples, C. Chilensis, Frembley, and C. Blainvillii, Broderip.
C. Chilrnsis. Shell oblong-ovate, opaque, thick, dirk brown, smooth, dull; inside white, with pink markings on the first, second, and last valves. Valves with longitudinal ntrire, crossed by irregular con centric) ridges. Anterior and posterior valves scmilunate, slightly punctated ; second valve subcarinated, the front margin obtusely angled, lateral margins arcuate, and the posterior with a prominent beak, on each aide of which diverges a rather elevated granulated ridge ; the next five valves alike, bow-shaped, with a granulate ridge on each aide. Border smooth, coriaceoua, tough, thick, darker coloured than the shell, semipellucid, broad at the sides and narrow at the extremities. Locality, Valparaiso, in crevices of rocks and under stones. (Frembley.) C. lJlainrillii. In this species the shape of the coriaceous border itself in not only very remarkable, but it is here and there fringed, though not with hair. 3L Deshayes has placed this under his section of those species which have the border of the mantle fringed with hair or spines, probably from not having soon a good specimen. Shell roundish, anterior valve obscurely rayed, the posterior one very small and abrupt ; the others concentrically lineated, the whole being rosy, variegated with white brown, and greenish, and internally white. The mantle-border orange-red, very narrow posteriorly, and enormously produced anteriorly, rounded and fringed here and there, especially on its anterior margin, with some short corisceoue Locality, Inner Lobos Island, coast of Peru.
O. Mantle-Border smooth, with tufts of hair at the lateral extremities of each plate.
C. fasciculuris, Linnaeus. Shell, apparently smooth, but when examined with a glass, proving to be rough like shagreen, except on the elevated dorsal ridge ; margin surrounded with tufts of whitish hair, one at the junction of each valve, and two in the front, making 18 in number. Colour brown or dark cinereous ; length iths of an inch ; breadth rather more than ith. Montagu, who gives this description, says, that on the coast of Barbary it is not unfrequently an inch long. It is found under stones at low water, and on stones and shells to a depth of 25 fathoms, all round the British shores. It ranges northward to the shores of Norway, and southward to the Mediter ranean. Some remains of Chiton in the Crag have been referred by Mr. Searles Wood to C. fasciculath.
7. Mantle-Border hairy.
C. Perurianus, Lamarck. Shell oblong-ovate, opaque, dirty yellowish, green, or yellowish-brown, inside white. Valves thin, slightly elevated; posterior compartments of the dorsal valves a little raised and striated, with minute granulated striae, and in like manner the other parts of the shell ; under each valve is inserted a series of short black hairs, which lie on the back of the shell. Border narrow, coriaceous, thickly set with coarse black
hairs. Length 2 inches, breadth 11 inch. Found under stones at low water on the shores of Valparaiso Bay. There is a variety with the anterior valves much narrower than the posterior. (Frembley.) 6. Mantle-Border beset with spines.
C. spinosus. Shell brownish-black, valves opaque, moderate, with the sides granulated, the anterior valves entirely granulated. Mantle border wide, and beset with long aculeated blackish spines, very much resembling those of certain Echini. Locality, South Seas, according to Pdron. Length 3 inches.
C. spiniferus (C. aculeatus, Barnes ; C. tuberculiferus, Sowerby, in ' Tankerville Catalogue'). Shell opaque, oblong ovate, reddish-brown, glossy ; inside reddish-white. The posterior angles of the valves do not cover the anterior ones. Anterior valve with generally nine rows of raised dots diverging from the apex, but the number perhaps varies with the age of the shell. Secondvalve rather acutely beaked and earinated, longer than the five following, which are striated and shaped alike ; these all rise into a rather acute beak, are carinated, each side of the earina being divided into two distinct portions, the anterior one the largest. and bearing broad irregular longitudi nal stria3; a prominent row of raised dots, extending from the apex to the anterior angles of the valves, separates the compart ments; the posterior portion glossy, with fine concentric striae ; the posterior margins with tooth like granulations. Last valve striated, like the anterior com partments of the others, and rising into a rather prominent beak, lean ing towards the posterior margin ; from under the beak are raised dots, disposed in a similar manner to those on the anterior valve. Border coriaceous, thick, broad, rough, greenish or orange coloured, and in the younger specimens thickly studded with blunt spines ; but in the old shells the spines are short and scanty, and generally covered with corcdlines ; the inner edge of the border, inserting itself under the posterior angles of the valves, has the appearance of being deeply separated. (Frembley.) This species grows to the length of 5 or 6 inches, but has then generally lost all its external beauty. We have seen many individuals in all the stages of growth, and have invariably found the spines of the aged ones covered with that calcareous matter which is so frequently found adhering to shells and submarine bodies, but we have never detected anything organic about that which was attached to the spines of this species. Locality, Chili and Valparaiso, where Mr. Frembley found several specimens in very exposed situations ; so much so, that collecting them was attended with much difficulty, and not unfre quently with danger, from the violence of the sea breaking on the rocks to which they attach themselves very strongly. They are generally covered with sea-weed.