Part 60

3. RINGICULA. Margin reflected. Fig. 540, 541.

PLICADOMUS. Sw. A sub-genus of Pupa, thus described: "spire moderate, regular and thick, but gradually conic; the tip obtuse; aperture perpendicular; inner lip wanting; outer lip semicircular; the margin dilated and reflected. P. sulcata, Chem. 135, f. 1231, 1232." Sw. p. 332.

PLICATED. (Plicatus, folded.) Applied to spiral plaits on the columella of some shells. Ex. Voluta, fig. 433. Also to the angular bendings in the margins of some bivalve shells. Ex. Dendostrea, fig. 181.

PLICATULA. Lam. (Plicatus, folded.) Fam. Pectenides, Lam. Sub-ostracea, Bl.--Descr. Irregular, sub-equivalve, sub-equilateral, attached by a small part of the surface of one valve, strongly plicated; umbones separated by a small, external ligamentary area; hinge with two cardinal teeth in each valve, two approximate in one valve, received between two distant in the other; cartilage placed between the cardinal teeth; muscular impressions one in each valve.--Obs. The cardinal teeth resembling those of Spondylus, distinguish this genus from others of the Lamarckian family Pectenides. Very few species are yet known, they are brought from the East and West Indies and the Philippine Islands. Fossil species are found in several of the supra-cretaceous beds. Fig. 178, P. gibbosa.

PNEUMOBRANCHIA. Lam. The second section of the order Gasteropoda, Lam. containing the family Limacinea, fig. 256 to 263.

PODOPSIS. Lam. This genus appears to have been described from specimens of a species of Spondylus, with the triangular disc broken out, so as to present a similarly shaped foramen, which was supposed to afford a passage for a large byssus.

POLINICES. Montf. A genus composed of NATICA Mammilla, and other similar species, with mammillated spires, and the umbilicus filled with enamel. Fig. 327.

POLLIA. Gray. TRITONIDEA, Sw. The name given by Gray was pre-occupied by a genus of Lepidopterous Insects.

POLLICIPES. Leach. (Pollex, a thumb's breadth; pes, a foot.) Order. Pedunculated Cirripedes, Lam.--Descr. Conical, compressed, consisting of numerous valves, mostly in pairs, three or four pairs forming the principal part of the shell, and surrounded at the base by two or three rows of smaller valves, supported on a scaly, short pedicle.--Obs. This description will be found to exclude Scalpellum, and Smilium, the valves of which are more equal. The P. Mitellus, Auct. (fig. 37*), has been separated as a genus under the name of Mitellus by some authors, and it is certainly very different from P. polymerus, fig. 37, and P. cornucopia.

POLLONTES. Montf. MILIOLA, Bl. A genus of microscopic Foraminifera.

POLYBRANCHIATA. Bl. ([Greek: Polus], polus, many; branchiæ, gills.) The fifth family of the order Lamellibranchiata, Bl. containing the genera Arca, Pectunculus and Nucula, which have a series of small teeth on the hinge.

POLYDONTES. Montf. ([Greek: Polus], polus, many; [Greek: odos], odos, tooth.) A species of Helix, shaped like CAROCOLLA, and having a number of teeth in the aperture.

POLYGONAL. Many-sided.

POLYGONUM. Schum. ([Greek: Polus], polus, many; [Greek: gônia], gonia, an angle.) A genus composed of species of TURBINELLA, Auct. which have large continuous costæ, so as to present the appearance of many-sided shells. T. polygonus, fig. 383. This generic name may be used to include all those species of Turbinella, Auct. which have very small folds on the columella.

POLYGYRA. Say. A genus of Heliciform shells, characterized by the large number of close set whorls, constituting the spire. Ex. P. Septemvolvus, fig. 275, 276.

POLYLEPAS. Bl. ([Greek: Polus], polus, many; [Greek: lepas], lepas, rock.) SCALPELLUM, Auct.

POLYMORPHINA. D'Orb. A genus of microscopic Foraminifera.

POLYPHEMUS. Montf. A genus composed of species of ACHATINA, Auct. which have elongated apertures, short spires, and an undulation in the outer lip. P. Glans, fig. 288.

POLYPLAXIPHORA. Bl. The second class of the sub-type Malentozoa, Bl. containing the genus Chiton.

POLYSTOMELLA. Lam. A genus of microscopic Foraminifera.

POLYTHALAMACEA. Bl. ([Greek: Polus], polus, many; [Greek: THalamos], thalamos, chambers.) The third order of Cephalophora, Bl. the shells of which are described as straight, more or less symmetrically convolute, divided into several chambers. The septa are sometimes, but not always, pierced by one or more siphons. This order is divided into the families, Orthocerata, Lituacea, Cristacea, Ammonacea, Nautilacea, Turbinacea, Turriculacea, all of which contain genera of chambered shells. De Blainville arranges these families according to the degree in which the spires revolve. The first being straight, as the Orthocerata, and the last being so closely coiled up, that the last whorl covers the rest, as in the Nautilacea.

POLYTHALAMIA. Lam. The first division of the order Cephalopoda, Lam. containing the following families of chambered shells, viz. Orthocerata, Lituacea, Cristacea, Sphærulacea, Radiolata, Nautilacea, Ammonacea. Fig. 463 to 484.

POLYTROPA. Sw. A genus of "Scolyminæ," Sw. thus described: "Bucciniform; but the base narrow, and ending in a straight and contracted, but rather short, channel; spire longer, or as long as the aperture; exterior folliculated, or tuberculated; inner lip flattened, as in Purpura; basal notch small, oblique; no internal channel; crispata. En. Méth. 419, f. 2. Chem. 187, f. 1802. Capilla, Pennant, pl. 72, f. 89, imbricata. Mart. 122. f. 1124. ? rugosa. Chem. f. 1473-4." Sw. p. 305.

POLYXENES. Montf. A genus of microscopic Foraminifera.

POMATIA. Gesner. (Gray, Syn. B. M. p. 133.) A genus of the family of "Cyclostomidæ," described as having "an elongated shell with reflexed lips, and a horny spiral operculum." Also a sub-genus of Snails, containing HELIX pomatia, Auct. (Gray's Turton, p. 135.)

PORNUS. Humph. AMPULLARIA, Lam.

PORCELLANA. Adanson. MARGINELLA, Auct.

PORODRAGUS. Montf. A genus composed of species of Belemnites, placed by De Blainville in the section characterized as swelled near the apex, and straightened towards the base.