There are reasons for believing the genus _Voluta_, as defined by Lamarck, to be typical of a natural group, comprising the genera _Mitra_, _Oliva_, _Ancillaria_ and _Marginella_. The obvious affinity between _Voluta_ and _Mitra_ need not be dwelt upon. The connexion of _Mitra_ with _Oliva_, we noticed in describing _Mitra olivæformis_, at pl. 48 of our first series. This affinity appears further strengthened by a shell in the late Tankerville Collection, especially recorded by Mr. G. Sowerby, as "remarkable for its resemblance to an Olive." We regret not having seen this shell, but such an authority is fully sufficient. The group of Mitres, by which this transision appears effected, is that mentioned under the head of _M. bicolor_ (Mitra, Pl. 1.) of this series. This little group has three relations: one to the smooth Mitres (as _M. pertusa_), another to _Conohelix_, and a third to the _Olives_: the species are all remarkable for the polished smoothness of their surface, for the total absence of the inner lip, and for the lower plaits of the pillar extending much beyond the aperture: these plaits, moreover, are generally five or six, and all very slender. The conchologist will perceive that nearly the only character wanting, to render this description applicable to an Olive, is the channelled groove round the suture. This character is added to the shell before us, which thus presents the first type of form in the present genus. Proceeding to the more perfect Olives, we observe the spire becoming gradually shorter; the vitrious deposition on the inner lip increased in thickness; the upper plaits on the pillar numerous, and those at the base thicker and more external (_M. fulmineus_, Lam. _elegans_, En. Meth. 362, 3.), the ventricose shape of some (_O. undata_, _inflata_, Lam.), the spire often concealed by a vitrious covering, and even the colours of others (_M. tessellata_, _guttata_) remind us of the typical Volutes. It is very remarkable, that in most of the cylindrical Olives, the apex is more or less, papillary: the last complete terminal volution of the spire being thick, inflated, and distorted: (see particularly _O. reticularis_, En. Meth. 36, f. 1; _fusiformis_, Ib. 367, 1; _guttata_, Ib. 368, f. 2.) Others are seen of a more slender form, as _O. subulata_, L. _acuminata_, E. M. 368, 3, where the pillar is similarly plaited. But in several small species allied to _O. conoidalis_, another modification of form has evidently commenced: the spire is regularly acute; the upper plaits disappear; and those which remain, are only at the thickened base of the pillar: the aperture, no longer narrow, becomes wide at the base, where the pillar takes an oblique direction inward: we are thus led to the form of _O. hiatula_, E. M. pl. 368, f. 5, where the characters of _Ancillaria_ become apparent in the effuseness of the mouth, the double belt at the base, and the imperfect groove on the outer side of the pillar. Whether we look to