RENIFORM. (_Ren_, a kidney; _forma_, shape.) Shaped like a kidney. _Ex._ The aperture of Ampullaria, fig. 318. RENULINA. Lam. A genus of microscopic Foraminifera. REOPHAX. Montf. A genus of microscopic Orthocerata, Bl. REPENT. (_Repens_, creeping.) A term applied to those shells, which, being attached by the whole length of their shell, give the idea of creeping or crawling. _Ex._ Vermilia, fig. 7. RETICULATED. (_Reticulatus._) Resembling net-work. RETIFERA. Bl. The first family of the order Cervicobranchiata, Bl. containing the genus Patella. REVERSED or SINISTRAL SHELLS, are those in which the aperture is on the left side of the shell, while it is held with the mouth downwards, and towards the observer. _Ex._ Balea, fig. 296. Attached bivalves are said to be reversed, when the left valve is free, instead of the right; a circumstance which sometimes occurs in Chama and Ostrea. RHEDA. Humph. HYALÆA, Lam. RHINOCLAVIS. Sw. A genus of "Cerithinæ," Sw. thus described: "channel curved backwards, in an erect position; inner lip very thick, with a tumid margin; pillar generally with a central plait; operculum ear-shaped; lineatum. En. M. 443, fig. 3, Vertagus. Ib. f. 2, subulatum. Lam. No. 23, fasciatum. Mart. 157, f. 1481. obeliscus, En. Méth. 443, f. 4; aluco, Ib. f. 5, (Aberrant,) semi-granosum. Ib. 443, f. 1, asperum. Mart. 157, f. 1483." RHINOCURUS. Montf. A genus of microscopic Foraminifera. RHINODOMUS. Sw. A genus of "Scolyminæ," Sw. thus described: No internal groove; shell clavate; the spire longer than, or equal with the aperture; the whorls with ridges or longitudinal varices, and rendered hispid by transverse grooves; inner lip wanting; pillar with a terminal fold; aperture striated; outer lip with a basal sinus. R. senticosus, Chem. tab. 193. f. 1864-1866. RHIZORUS. Montf. A genus described from a microscopic shell, appearing to be a cylindrical Bulla. RHODOSTOMA. Sw. A sub-genus of "Turbininæ," Sw. p. 344. RHOMBOIDAL. ([Greek: rhomboeidos], _rhomboeidus_.) Having a rhombic form, i. e. four-sided; two sides meeting at acute, two at obtuse, angles. Conchologists are not very strict in the application of this term, for, indeed, a perfect rhomboidal figure could not be found among all the testaceous productions of the sea. RHOMBOIDES. Bl. A genus described as resembling Byssomya in the shell, but differing in the animal. MYTILUS rugosus, Gmelin. HYPOGÆA barbata, Poli. RHOMBUS. Montf. ([Greek: rhombos], _rhombos_, a rhomb.) A genus consisting of species of CONUS, having a rhomboidal or quadrilateral form and a coronated spire. _Ex._ Conus nocturnus, fig. 459.