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._ [Illustration: 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_.