PANOPÆA. Menard. _Fam._ Solenacea, Lam. Pyloridea, Bl.--_Descr._ Equivalve, inequilateral, oval, gaping at both extremities; hinge with an acute cardinal tooth in each valve, and a large callosity near the umbones supporting the ligament; muscular impressions two, distant, oval; palleal impression with a large sinus. Britain, North America, Mediterranean, Australia, &c.--_Obs._ This genus resembles Mya in general appearance, but differs in having an external ligament and a sharp tooth, instead of the broad spoon-shaped process in the hinge of the latter genus. Fig. 65. P. Australis. PAPER SAILOR. A common name given to the Argonauta. PAPILLARY. (_Papilla_, a teat.) Shaped like a teat. This term is applied by conchologists when the apex of the spire of an univalve shell is rounded like a teat and not spiral up to the extreme point; as the apex of Cymba, fig. 434. PAPYRACEOUS. (_Papyrus_, a kind of paper made of the flags of the river Nile in Egypt.) Of a thin, light texture, resembling that of paper. An example of this is to be seen in the Argonauta, commonly called the "Paper Sailor," fig. 485, and in the Pholas papyracea, fig. 56. PAPYRIDEA. Sw. A sub-genus of Cardium, thus described; "Shell heart-shaped, or transversely oval; inequilateral; the anterior side almost always gaping; representing the Pholidæ. P. Soleniforme, Wood, Conch. pl. 56. f. 3.--apertum, Ib. 56. f. 2.--transversum, Sow. Conch. f. 4.--ringens, Wood, pl. 53. f. 1, 2." PARACEPHALOPHORA. Bl. The second class of the type Malacozoa, Bl. divided into the sub-classes: P. dioica, P. monoica, P. hermaphrodita. PARIES. (_A wall._) The principal part of a multivalve shell, forming a circular wall round the body of the animal, and composed of one or more valves which are called the parietal valves. PARIETAL VALVES. The principal valves of multivalve shells surrounding the body like a wall; as distinguished from the opercular valves, or those which compose the operculum. PARMACELLA. Cuv. (_A little cell._) _Fam._ Limacinea, Lam. and Bl.--_Descr._ Haliotoid, internal, thin; spire flat, consisting of one or two rapidly increasing whorls; aperture as large as the whole shell, with the dorsal margins inflected.--_Obs._ This description applies to Parmacella of Cuvier. The shell figured in Sowerby's Genera under that name is Cryptella of Webb. Fig. 257, P. Olivieri. Fig. 258, P. Palliolum. PARMOPHORUS. Bl. A genus composed of EMARGINULA elongata, Auct. and other species of a similarly elongated form. Australian. Fig. 242. P. elongatus.