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.