POL 



[ 363 ] 



P R 



POLYPOTHE'CIA. A genus of spongeous 

 zoophytes found in flints, and thus 

 named by Miss Bennett, of Korton 

 House, near Warminster. 



POLY'PTERUS. A genus of fishes found 

 in the Nile and in the rivers of 

 Senegal. The Polypterus and Le- 

 pidosteus are the only known 

 genera of living representatives of 

 the sauroid fishes. 



POLYSP'ERMOUS. (from TroXvs, many, 

 and mrepfia, seed, Gr.) In botany, 

 a term applied to the ovarium and 

 fruit, when they contain many 

 seeds. 



POLYTHA'LAMOUS. (from TTO\VS, many, 

 and 6d\afio<s, a chamber, Gr.) 

 Having many cells or chambers, 

 as polytJialanwus shells ; multilo- 

 eular; camerated. 



POLYZO'A. Called also Bryoza: the 

 second order of the class Mol- 

 luscoidea, comprising flustra, rete- 

 pora, eschara, and other zoophytes. 



PO'RCELAIN EARTH. | For a descrip- 



PO'RCELAIN CLAY. ) tion of this, 

 See China Clay. 



PO'RCELAIN JAS'PER. A variety of 

 jasper ; called also Porcellanite. 

 see Porcellanite. 



PGRCELANA'CEOUS. | Resembling por- 



PORCELA'NEOUS. ) celain. Shells 

 have been divided into two classes. 

 The first are of a compact texture, 

 have an enamelled surface, and are 

 generally beautifully variegated ; 

 the shells of this class have been 

 termed porcelanaceous, or porcela- 

 neous shells; they contain but a 

 small proportion of soft animal 

 matter. 



PORC'ELAINOTJS. The name given to a 

 species of protogine. Porcelainous 

 Protogine, or China Stone, is com- 

 posed of felspar quartz and talc, 

 and is of a greenish-yellow colour. 

 It affords, by decomposition, the 

 china clay of commerce. 



PORCE'LLANITE. The Porzellan Jaspis 

 of Werner; Thermautide porcel- 

 lanite of Haiiy; Porcellanite of 

 Kir wan. This is a variety of 



Jasper, according to some miner- 

 alogists ; Prof. Jameson places 

 it as a sub-species. Mr. Allan, 

 however, says "it is merely clay 

 indurated by heat ;" and according 

 to Werner, it is siate-clay converted 

 into a kind of porcelain by the 

 action of the heat of the volcano. 

 "A mineral of various colours, 

 from grey to nearly black, occur- 

 ring in amphorous masses or frag- 

 ments, which are often rifted. 

 Porcellanite sometimes resembles a 

 brick which has undergone a slight 

 vitrification. Its fracture is im- 

 perfectly conchoidal or uneven, 

 more or less glistening, and often 

 has the aspect of certain porcelains. 

 It is opaque, very brittle, and less 

 hard than quartz. An analysis, of 

 of it yielded silex 60 '75, alumine 

 27'25, potash 3 66, magnesia 3, 

 oxide of iron 2 '50. It is most 

 likely an alteration of some variety 

 of argillaceous slate by pseudo- 

 volcanic fires : it does not con- 

 stitute a distinct species. It is 

 found in large masses near the 

 pitch-lake in Trinidad, and occurs 

 usually in the vicinity of coal 

 mines." Cleaveland. 

 POR'CELAIN SPAR. A mineral combi- 

 nation with a chloride, consisting 

 of four equivalents of the double 

 silicate of lime and alumina with 

 one of chloride of sodium. 

 PORI'FERA, | (from porus, a pore, 

 PORI'PHERA. ) and fero, to bear.) 

 A classs of animals belonging to 

 Cyclo-]X"eura, or Radiata. Pori- 

 phera constitutes the second lowest 

 class of animals, coming between 

 PolypipheraandPolygastrica. They 

 form the various species of sponge 

 which are met with in such mul- 

 titudes on every rocky coast of the 

 ocean, from the shores of Greenland 

 to those of Australia. Their sur- 

 face is porous ; those pores lead to 

 canals which ramify through all 

 parts of their texture ; and those 

 canals anastomosing into larger and 



