_Aperture_, or mouth, is that part of the lower whorl or body by which the animal protrudes itself. This is one of the principal generic distinctions of Univalve shells, and differs very much in shape; some apertures being rounded, others semilunar, angular, &c. Plate II. figs. 9 and 11, _C C_; and Plate III. figs. 1, 3, and 14, _C C C_. Some apertures have a canal at their base, and others are devoid of it. In various genera it extends the whole length of the shell, as in the Cypræa, and some of the Cones with depressed spires. This in several individuals is either entirely open, or is closed by an operculum or lid, which is usually affixed to the foot of the animal. _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.