Canal, or gutter, is the inside of the elongations of the aperture, or both lips of the shell of those species with a beak, in which it forms a concave channel or gutter, running from its commencement in the aperture to the extremity or base. Plate [II]. figs. 10 and 11, Q Q. Plate [III]. fig. 8, Q. Some species are furnished with two canals, one situated at the junction of the outer lip and body, as in the Murex.
Beak is that lengthened process in which the canal is situate; it commences a little higher up, on the outside, than the insertion of the canal in the inside, which is always distinctly marked by the line of the aperture. Plate [II]. fig. 11, p. This process is not so conspicuous in some of the species of Voluta, but is more marked in the genera Murex, Fusus, Pyrula, &c.
Pillar, or columella, is that process which runs through the centre of the shell in the inside from the base to the apex in most univalve shells, and appears to be the support of the spire: and, indeed, seems to form that part of the shell: it is in general grooved or folded; but, as it is situated in the interior of the shell, a minute description is unnecessary. Plate [II]. figs. 10 and 12, M M M M M; and Plate [III]. fig. 9, M M M. The internal edge of its base is frequently described as having plaits, &c.
Plaited Columella are those folds, or plaits, which are the distinguishing characteristic of the Volutæ and other genera. Plate [II]. fig. 7, z.
Pillar Lip is a continuation of the glossy process with which the aperture is lined, and expanded on the columella. Plate [III]. figures 7 and 8, O O. This is termed the inner lip by some authors.
Outer Lip. The expansion, or continuation of the body of the shell on the left margin of the aperture, and is also lined with the glossy process of the aperture. Plate [II]. fig. 7, N; and Plate [III]. fig. 8, N N N. The latter is an example of the alated or winged shells.
Operculum, or lid. This is only an appendage to the turbinated or spiral shells affixed to the foot of the animal, sometimes of a testaceous, in others of a horny or cartilaginous substance. It acts as a door or lid, and is calculated for the protection of the animal, when it retires within its dwelling, from the intrusion of its enemies, and adapted to the shape of the aperture, which it closes nicely up: as exemplified in the operculum of the Turbo, and is of a hard, stony appearance. Plate [III]. fig. 4.
Spire consists of all the whorls of the shell, except the lower one, which, as before observed, is termed the body of the shell. Plate [II]. fig. 12, D; and Plate [III]. figures 7 and 8, D D.
The spire is a prominent feature of the Univalve; and upon its being elevated, depressed, &c., depends much of the generic and specific definition. Adanson, in his ‘Natural History of Senegal,’ says that the external character of the spire varies according to the plane they turn upon, which, he observes, is either horizontal, cylindrical, conic, or ovoid. At the same time, he admits that there are a great many intermediate forms which cannot properly be defined.
It must be remembered that many of the young shells have not the same number of wreaths as the adults; from which it would appear, that the part of the animal nearest the apex never increases in size. The number of wreaths cannot, at all times, be depended upon. A full grown shell may, however, be known from the outer lip, which has generally an unfinished appearance in young shells. Indeed, in all the land and fresh water shells it is a distinct criterion, as they are never complete in the form of the outer lip till full grown.