Part 52

NYMPHACEA. Lam. A family belonging to the order Conchifera Dimyaria, Lam. Ligament external, placed on a prominent fulcrum. This family contains the following genera:

1. SANGUINOLARIA. Rostrated, gaping; two cardinal teeth in each valve, including Soletellina and Lobaria. Fig. 98, 99.

2. PSAMMOBIA. Quadrate; valves closed, including Psammotæa. Fig. 100.

3. CORBIS. Thick, fimbriated; a cardinal tooth in the centre of a pit. Fig. 101.

4. GRATELOUPIA. A series of small teeth filling a triangular area. Fig. 102.

5. EGERIA. One single and one double cardinal tooth. Fig. 103.

6. LUCINA. Rounded; anterior muscular impression tongue-shaped. Fig. 104.

7. TELLINA. An anterior fold in the ventral margin; lateral teeth. Fig. 105, 106.

8. TELLINIDES. No anterior fold; no lateral teeth. Fig. 107.

9. DONAX. Margin denticulated; shell wedge-shaped. Fig. 108.

10. CAPSA. Margin not denticulated, no lateral teeth. Fig. 109.

OBELISCUS. Humph. TROCHUS, Lam.

OBLIQUE. (obliquus. lat.) In a slanting direction. The whorls of spiral univalves generally take an oblique direction in reference to the imaginary axis of the shell. A bivalve is said to be oblique when it slants off from the umbones. An example of this is seen in Avicula, fig. 163.

OBSOLETE. (obsoletus, lat.) Worn out, out of use. This term is used to express an indistinctness of character, which sometimes results from the action of sea-water upon unprotected parts of the shell, and sometimes from the deposits of enamel formed in age, and covering the early striæ, ribs, teeth, &c. thereby rendering them less acute.

OBTUSE. (obtusus, blunt.) The application of this term is not peculiar to conchology. It is most frequently used to express the character of the spire. Ex. The apex of Megaspira, fig. 294.

OCEANUS. Montf. ("Corne d'ammon vivant," Fr.) NAUTILUS umbilicatus, Auct.

OCTHOSIA. Ranz. CLITIA, Leach.

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.

ONISCIA. Sow. (G. B.) Fam. Purpurifera, Lam. Entomostomata, Bl.--Descr. Oblong, sub-ovate, slightly turbinated, cancellated; spire short; aperture elongated; terminating anteriorly in a very short, recurved canal; outer lip thickened, denticulated within; inner lip spread over a portion of the body whorl, granulated.--Obs. The granulated inner lip is the principal character by which this genus is distinguished from Cassidaria. In Oniscia the canal is not so produced. O. oniscus, fig. 409.

ONUSTUS. Humph. A genus proposed by Humphrey and adopted by Swainson who describes it thus: "Shell trochiform; the surface irregular, and often covered with extraneous bodies, cemented and incorporated with the calcareous substance of the shell; the under part of the body whorl flattened or concave, umbilicate. O. Solaris. Mart. 173. f. 1700, 1701. Indicus. Ib. 172. f. 1697. 1698." It is probable, from the above description, that Mr. Swainson intended to include Trochus agglutinans of authors. (Genus Phorus, Montf.) Fig. 360.