230 PARIETAL VALTES. 



danger of being confounded with any other shell. P. rostrata, 

 PL iv. fig. 90. 



PAJ^OP^A. Menard. Fam. Solenacea, Lam. Pyloridea, Bl. — 

 Bescr. 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, &e. 

 — 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. P. Australis. PI. iii. fig. 65, 66. 



PAPEE SAILOE. A common name given to the Argonauta. 



PAPILLAEY. {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 Gymba, fig. 434. 



PAPYEACEOUS. {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 caUed the " Paper Sailor," fig. 485, and in the Pholas 

 papyracea, fig. 56. 



PAPTEIDEA. Sw. A sub-genus of Cardium, thus described ; 

 " Shell heart-shaped, or transversely oval ; inequilateral ; the 

 anterior side almost always gaping ; representing the Pholadae. 

 P. Soleniforme, "Wood, Conch, pi. 56. f. 3. — apertum, lb. 56. 

 f. 2. — transversum, Sow. Conch, f. 4. — ringens, "Wood, pi. 53. 

 f. 1, 2." PL xxiv. fig. 503, 504. 



PAEACEPHALOPHOEA. BL The second class of the type 

 Malacozoa, Bl. divided into the sub-classes : P. dioica, P. mo- 

 noica, P. hermaphrodita. 



PAEIES. {A wall.) The principal part of a multivalve sheU, 

 forming a circular wall round the body of the animal, and com- 

 posed of one or more valves which are called the parietal 

 valves. 



PAEIETAL VALVES. The principal valves of multivalve shells 



