interrupted by any thing known: this latter shell resembles the true _Rostellariæ_, but with the digitated processes of _Pteroceras_ reduced to teeth; which teeth, in _R. curvirostris_, become confined to the basal part of the unexpanded lip. We are here met by certain fossil shells, preserving the form of _Rostellaria_, but with the outer lip entire, and sometimes considerably expanded: in these the spiral canal sometimes extends to the summit of the shell: finally the distinct sinus again appears in such species as _S. cancellatus_, _canalus_, &c., all which have been classed by conchologists with _Strombus_. This series is sufficient to shew the _tendency_ of a circular disposition of relations, but very many of the intermediate forms are wanting, nor is it at all clear in what way the immediate passage is effected between _Hippochrenes_ and the genuine _Strombii_. * * * * * * [Illustration: OLIVA. Pl. 1. _1. volutella 2. striata_] OLIVA volutella. ---- Class Mollusca. Order Zoophaga. _Lam._ Genus Oliva. _Lam. Sys. 7, p. 416._ ---- SPECIFIC CHARACTER. _Shell ovate-conic, mitriform; chestnut, the body whorl bluish; spire lengthened, acute; pillar with 6-7, slender, regular plaits._ Oliva volutella. _O. testâ ovato-conicâ, subcæruleâ, ad spiram basimque luteo fuscatâ; spirâ valdè productâ, acutâ._ Lam. Sys. 7, 1, p. 432. ---- We are indebted to the Rev. Mr. Bulwar for our specimens of this elegant and highly interesting species, received by him from the American Isthmus. It varies much in the intensity of its colour, as may be seen from the above description, given by Lamarck, of examples procured by Baron Humbolt on the shores of Mexico.