A conchological manual

by G. B. Sowerby

When there is neither notch nor canal, anteriorly or posteriorly, interrupting the edge of the aperture, it is described as entire. When there is a notch or sinus at the anterior extremity, it is said to be emarginated. When the edge of this notch is expanded, and drawn out in the form of a beak, it is said to be canaliferous, or to have a canal. When, in addition to this, the lips are thickened and contracted posteriorly near their junction, and drawn out so as to form a groove, it is said to be bi-canaliculated, or to have two canals. The anterior canal is said to be long or short, according to the proportion which it may bear to the rest of the shell. Thus the canal of Ranella ranina (fig. 393 in the plates), may be described as short; while that of Murex haustellum, (fig. 396, pl.) is long. When it is wide near the aperture, and becomes gradually contracted towards its termination, it is said to be tapering, as in Pyrula (fig. 388, pl.); when the termination is sudden, it is described as truncated. If, on placing the shell upon a plane, with the aperture downwards, the canal is seen to rise upwards, it is recurved. In Buccinum and Nassa it is turned suddenly over the back, and forms a short, curved elevation; it is then described as recurved and varicose. If the edges meet, so as to form a tube, it is said to be closed, as in some species of Murex and Typhis. The posterior canal is, in some cases, free, or standing out from the spire, as in some species of Ranellæ; while in others it is decumbent, running up the sides of the spire, as in Rostellaria (fig. 402, pl.).

Canals.

Fig. 51, Fasciolaria, truncated; 52, Nassa, recurved, varicose; 53, Cerithium, recurved; 54, Typhis, closed.

Lips, or edges of the Aperture.

The part of the edge of the aperture next to the body whorl is named the inner, or columellar lip. Posteriorly it commences at the point of union with the outer lip, where that touches the body whorl, the junction being generally marked by an angle, and sometimes by a canal. Anteriorly it terminates where there is generally seen a notch or canal, or sudden angle, from which the outer lip proceeds. The part which setting out from the body whorl, and proceeds outwards at a distance from the axis, till it reaches the anterior canal or notch (or its place in case of absence) is named the outer lip. In many cases the edges are united in such a manner, that it is difficult to distinguish where the inner lip terminates, and the outer lip commences: when this is the case, it is usual to describe the margin or peritrême, as a whole, without distinguishing the parts. The outer lip, sometimes called the right lip, or labrum of continental writers, is sometimes acute, not being of thicker substance than the remainder of the shell. In other cases it is obtuse, or thickened and rounded at the edge. When thickened and turned backwards it is described as reflected; when, on the other hand, it is turned inwards towards the axis, as in the Cyprædæ, it is inflected, or involute. When it is toothed, a distinction must be observed as to whether the dentations are external or internal. If the teeth are small and numerous, it is denticulated; if larger, it is dentated; when expanded into a kind of wing, as in some species of Strombus and Rostellaria, it is described as alated; and a family in Lamarck's system is named "Alatæ," from this very circumstance. In some of those which are expanded, the expansion is divided into separate, attenuated portions, they are then said to be digitated.

Outer Lips.

Fig. 55, Helix, reflected; 56, Cypræa, involute, denticulated; 57, Sera, alated; 58, Murex, digitated; 59, Rostellaria, dentated.

The inner lip, sometimes named the columellar lip, or "labium," is subject to similar variations as to thickness, dentition, &c. That portion of it which lies upon the body-whorl is frequently distinguished from that which intervenes between it and the notch or canal. De Blainville, restricting the term lip "bord gauche" to the former portion, applies the term "columella" to the latter; and in some instances this may be the more convenient method of describing the part in question. The columellar lip is sometimes detached entirely from the body of the shell, as in Murex haustellum; in others it is decumbent, or lying over the last whorl, although quite distinct, and in some cases, thickened, callous, or tumid.