OCTOCERA. Bl. The first family of the order Cryptodibranchiata, Bl. containing the genus Octopus. A species of which being found in the Argonauta, or Paper Sailor, has given rise to the long continued controversy as to whether it is really the constructor of the shell, or whether it is a mere pirate, and having destroyed the true animal of the Argonaut, has possessed itself of the habitation. This question is now set at rest. See ARGONAUTA. OCTOGONAL. (_octogonum._) Having eight angles. For an example, see Dentalium, fig. 2. OCTOMERIS. Sow. ([Greek: oktô], _octo_, eight; [Greek: meros], _meros_, part.) _Fam._ Balanidea, Bl. _Order_, Sessile Cirripedes, Lam.--_Descr._ Eight principal valves circularly arranged, forming a compressed cone, attached by a jagged base; aperture enclosed by an operculum, consisting of four valves in pairs.--_Obs._ The only genus of Sessile Cirripedes agreeing with this in the number of principal valves is Catophragmus, Sow. which is, however, sufficiently distinguished by the several rows of smaller valves by which the principals are surrounded at the base. O. angulosus, fig. 24. ODONTIS. Sow. MONODONTA, Lam. ODOSTOMIA. Flem. _Descr._ "Shell conical; aperture ovate; peristome incomplete, retrally, and furnished with a tooth on the pillar." A genus composed of several small species of land shells. Turbo plicatus, Spiralis, Unidentatus, &c. Mont. OLIVA. Auct. (_An olive._) _Fam._ Convoluta, Lam. Angyostomata. Bl.--_Descr._ Oblong, cylindrical, thick, smooth, shining; spire very short, with sutures distinct, aperture elongated, notched at both extremities; outer lip generally thick; columella thick, obliquely striated, terminated by a tumid, oblique, striated varix; a raised band passing round the lower part of the body whorl.--_Obs._ The shells composing this well known genus present a great variety of rich markings and brilliant colours. They are marine and tropical. Fossil species are found sparingly in the London Clay and Calcaire-grossièr. The Ancillariæ are distinguished from this genus by the sutures of the whorls being covered by enamel. O. maura, fig. 457. OLIVELLA. Sw. A genus of "Olivinæ," Sw. thus described: "Oliviform; spire (typically) rather produced; the tip acute; inner lip not thickened; outer lip straight; base of the pillar curved inwards, and marked by two strong plaits; upper plaits obsolete or wanting; aperture effused at the base only; biplicata, Tank. Cat. 2332. purpurata. Zool. Ill. ii. 58. f. 1. mutabilis. _Say._ eburnea. Zool. Ill. ii. 58, f. 2. conoidalis. _Lam._ No. 57. oryza. _Lam._ No. 62." OLYGYRA. Say. Mentioned by Ranz as properly belonging to Helicina. H. neritella, Auct. OMALAXIS. Desh. Subsequently BIFRONTIA. Desh. Fig. 354.