ROSTELLARIA. _Lam._ Outer lip dentated, but not dilated. Basal canal long. HIPPOCHRENES. _Montf._ Outer lip generally dilated, and always entire. Basal canal moderate or short. Spiral canal nearly equal to the spire. _Rost: macroptera, columbata, fissurella, Lam._ ---- SPECIFIC CHARACTER. _Basal canal short: spiral canal thickened, and perpendicularly ascending on the spire._ Strombus fusus. _Linn. Gm. 3506. Lister, 854, 12. Seba, 3, 56, 1._ Rostellaria curvirostris. _Lam. Sys. 7, 1, 192. Ency. Meth. pl. 411, f. 1._ ---- This elegantly formed shell is a native of the Red and Indian Seas. It is the most common of the few species retained in the genus _Rostellaria_; all these are recent; while _Hippochrenes_ has occured only in a fossil state. The preceding table of affinities, connecting the leading forms among the _Strombii_, will be adverted to hereafter. At present we shall offer a few observations on the nature of that more comprehensive division of the class _Mollusca_, to which this particular group appears to belong. The learned Author of the Horæ Entomologicæ, in that part of his valuable essay relating to the _Molluscæ_, considers our knowledge of these animals too imperfect to enable him to state the nature of the typical groups: the situations of which, in his diagram of the animal kingdom, are therefore merely indicated by stars. M. Macleay further remarks, that the _Gasteropoda_ of M. Cuvier, with certain restrictions, evidently form a circular group. Yet, from the above omission, it appears he still entertained some doubts on the propriety of this arrangement. Labouring under similar disadvantages to those which impeded the researches of so profound an observer, we feel some hesitation in expressing a different sentiment on the subject, particularly in reference to his own disposition of affinities.