214 PALUDOMUS. 



P. major. Mart. 163. f. 1541, 1542. tectum-persicum. lb. f. 

 1543, 1544." Sw. p. 351. 



PALLEAL IMPRESSION. {Pallium, a mantle.) The mark or 

 groove formed in a bivalve shell by the muscular attachment of 

 the mantle, which, being always found near the margin of the 

 shell, is sometimes termed the marginal impression. In bivalves 

 with two muscular impressions it passes from one to the other. 

 If in passing, it takes a bend inwards posteriorly, it is said to be 

 sinuated, and that part is called by Mr. Gray, the Siphonal scar. 



PALLIOBRANCHIATA. Bl. The first order of the class Acepha- 

 lophora. Bl. The animals of this order are described as more 

 or less compressed, included between the two valves of a 

 bivalve shell, one inferior, the other superior, joining at the back 

 and opening in front. The Palliobranchiata in the system of De 

 Blainville correspond with the Brachiopoda in the system of 

 Lamarck, and the shells may be known by their being symme- 

 trical. This order contains in the first section of symmetrical 

 bivalves, Lingula, Terebratula, Thecidium, Strophomena, Plagio- 

 stoma, Dianchora and Podopsis : in the second section, Orbicula 

 and Crania. 



PALMATED. Flattened like a palm, as the fronds or fringes of 

 some Murices. 



PALMINA. Gray. Differing from Otion in having but one 

 auricle. 



PALUDINA. Lam, Fam. Peristomata, Lam. Cricostomata, Bl. — 

 Descr. Varying in form from oval to globose, in some instances 

 oblong, covered with a greenish horny epidermis ; spire acute, 

 composed of rounded whorls ; aperture ovate ; peritreme entire, 

 slightly modified by the last whorl ; operculum horny, concen- 

 tric. Europe, North America, East Indies, China, &c. — Obs. The 

 construction of the operculum distinguishes this genus of fresh- 

 water shells from Valvata and Cyclostoma. The Paludinse are 

 viviparous. Fig. 321. P. Achatina. 



PALUDOMUS. Sw. A genus of the family of " Melanianse," 

 Sw. described as differing from Melania in having the spire 

 shorter than the aperture. Sw. p. 340. 



