| Term | Definition |
| COMMARGINAL RIB | [need definition]; see also: OVERRIDE. | |
| PROVINCE, CARIBBEAN | A warm-water region centered in the West Indies, extending north to the Florida Keys and Bermuda, and southward to Brazil. Characteristic species are the QUEEN CONCH, Wide-mouthed Purpura and the Sunrise Tellin; see also: PROVINCE, (types). | |
| RADULA RIBBON | The flexible structure in which the radular teeth are embedded; see also: RADULA. | |
| RIB, AXIAL | [need definition]. See illustration: Composite Gastropod. See also: SCLEROCHRONOLOGY; VARIX. | |
| RIB, CONCENTRIC | A RIB that follows COLLABRAL LINES. See illustration: Composite Bivalve. | |
| RIB, DIRECTIVE | A rib, forming a part of surface ornament of a shell, that lies entirely within a single plane; see also: DIRECTIVE SPIRAL. | |
| RIB, DIRECTIVE | A RIB, forming part of surface ORNAMENTATION of shell, that lies entirely within a single plane. | |
| RIB, LABIAL | A varix; a thickened or extensive AXIAL RIB. | |
| RIB, LONGITUDINAL | [need definition]. See illustration: Composite Gastropod. | |
| RIB, RADIAL |
A RIB emanating outward from a central point of origin, usually along with other ribs. See illustration: Composite Bivalve. Photo: Anadara ovalis (Bruguiere,1789) |
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| RIB | A raised, elongate structural element, generally axially oriented; see also: RIB, (types); RIB-STRIAE; RIBLET; RIPPLED; STRIAE; VARIX. | |
| RIBBED | Having RIBS. | |
| RIBLET | A minor rib; see also: STRIAE. | |
| RIBLET, PRIMARY | On shell with riblets of different orders of strength, the riblet that appears early in ontogeny and remains longer than those appearing later; see also: RIBLET, SECONDARY. | |
| RIBLET, SECONDARY | On shell with riblets of different orders of strength, the riblet that appears somewhat later in ONTOGENY than primary riblets and remains weaker than these; see also: RIBLET, PRIMARY. | |
| RIB-STRIAE | Transverse undulations of the shell surface which are more prominent than STRIAE but less prominent than RIBS; see also: STRIAE; RIB; RIBLET. | |