RICINULA. Lam. (Resembling the seed-vessel of the _Ricinus_.) _Fam._ Purpurifera, Lam. Entomostomata, Bl.--_Descr._ Sub-ovate, thick, tuberculated; spire short; aperture narrow, terminating anteriorly in a short canal; outer-lip thickened, denticulated within, digitated without; columellar lip spread over a portion of the body whorl, and granulated.--_Obs._ This interesting genus is composed of some neat little shells allied to Purpura, from which they are distinguished by the finger-like branching of the outer lip, and the granulations of the columella. Fig. 413, R. Horrida. RIGHT. See DEXTRAL. RIMULA. Defr. A genus consisting of a minute species of EMARGINULA, Auct. which has a fissure near the margin, but not reaching it. R. Blainvillii, fig. 243. RIMULINA. D'Orbigny. A genus of microscopic Foraminifera. RINGICULA. Deshayes. A genus founded on Auricula ringens of Lamarck and several small fossils, resembling in some respects Pedipes of Adanson; they would belong to Tornatella, were it not for the lips being thickened and marginated, fig. 540, A. ringens. RISSOA. Freminville. _Fam._ Ellipsostomata, Bl. Melaniana, Lam.--_Descr._ Oblong, turrited, acuminated; spire long, consisting of numerous whorls; aperture round or oval, pointed posteriorly, dilated anteriorly; outer lip slightly thickened, emarginated, operculum horny.--_Obs._ The Rissoæ are small white, marine shells, considered by some authors as resembling Melaniæ, but placed by Sowerby near the Scalariæ. They are principally from the shores of the Mediterranean, and are also very abundant on the British shores, as well as the East and West Indian. Fig. 346, R. reticulata. ROBULUS. Montf. A genus of microscopic Foraminifera. ROLLUS. Montf. A genus composed of CONUS Geographus, Auct. fig. 462, and other species, rather cylindrical in form, and having a coronated spire. ROSALINA. D'Orb. A genus of microscopic Foraminifera. ROSTELLARIA. (From _rostrum_, a beak.) _Fam._ Alatæ, Lam. Siphonostomata, Bl.--_Descr._ Turrited, fusiform, thick, smooth or ribbed; aperture oval, terminating anteriorly in a long canal, posteriorly in a channel running up the spire; outer lip dilated, thickened, sometimes digitated, running up all or part of the spire, with a sinus near the anterior canal; inner lip smooth, spread over part of the body whorl and of the spire. The Red Sea and the Indian Ocean produce the few known species of this genus.--_Obs._ HIPPOCHRENES is the name given by De Montfort, to those fossil species which have the outer lip simple and very much dilated. R. curvirostrum, fig. 412. APORRHAIS is a name given to another proposed genus, composed of Rostellaria pes-pelecani, Auct. fig. 404. and similar species.