A very singular shell, greatly resembling a petrified body, composed of a testaceous white substance like alabaster. The base is bent into a short spire, with about four contiguous whorls; the last prolonged and nearly straight. The animal, as it increases in size, abandons the spiral part by increasing the tubular part, filling up the part it quits with calcareous matter, which proves that it advances gradually.
Tube partially involuted, convex in its upper exterior part, the lower side flattened, platted, carinated, and somewhat angular; the spire short, helix-formed, and prolonged through the rest of its extent in nearly a right line; aperture entire, oval, with a sort of sinus or gutter in the middle line, producing the keel of the shell.
M. antiquus. The antiquated Magilus.
Answers to the above description; colour pale yellowish brown, transversely wrinkled.
CLASS II.
CIRRHIPEDES.
HAS BUT ONE FAMILY.
Cirrhipedes. Ten genera.
Lamarck divided the Lepas of Linnæus into the various genera which compose this family. The term lepas is derived from the Greek word λεπας, a rock, alluding to its custom of adhering to rocks and marine bodies. The shell often varies in shape, covering, and colouring; it is generally conical, but sometimes hemispherical; some of the valves are placed perpendicularly on a base, broad at the lower margin and tapering towards the summit, which is closed by small horizontal valves forming the operculum. The number of valves is indefinite, from four to twenty-four; but all are diversified with striæ, ridges, and grooves. The striæ are mostly transverse, and the ridges longitudinal.
The valves which compose the operculum or lid vary in shape, and are in number two, three, four, or more; they are generally attached to a ligament.
They are seldom, if ever, found detached, but adhere in groups to rocks, shells, anchors, marine animals, &c. Those that fix themselves to ships are generally called barnacles; they rapidly increase in size and number, do great damage, and greatly impede the progress of the vessel. Some of this family are affixed at the base of the shell to other substances, and are therefore called sessile; others are attached to a fleshy peduncle or stem, and are said to be pedunculated. The peduncle or stem, proceeding from the base of the shell to the substance which sustains it, is sometimes smooth, fine in texture, and tinged with bright red or orange; sometimes it is of a dark or brownish colour, with a texture much coarser and granulated.