PET 



[201 ] 



P H O 



stalk, or stem, which connects the leaf 

 with the branch. 



PETRI'COLA. (from Trerpoc, a stone, Gr. 

 and cplo, to inhabit, Lat.) A genus of 

 transverse, inequilateral, bivalve, marine 

 shells, belonging to the family Lithophagi. 

 Two muscular impressions ; two hinge- 

 teeth on one valve, and a bifid one on the 

 other ; anterior side rounded, posterior 

 side more or less slightly gaping ; liga- 

 ment external. Petricolse are found at 

 depths varying to ten fathoms ; they 

 inhabit cavities, of their own working, in 

 rocks and shells. They may be distin- 

 guished from saxicava by the regularity 

 of their form, and by the teeth on the 

 hinge, which in saxicava become obsolete 

 when the animal is full grown. 



PETRIFA'CTION. (petrifaction, Fr.) A 

 substance converted into stone. Sub- 

 stances, either animal or vegetable, con- 

 verted into stone by the infiltration, or 

 incrustation, of siliceous matter. 



PETRE'SCENT. (from petrescens, Lat.) 

 Becoming stone ; growing into stony 

 matter. 



PETRO'LEUM. (petrole, Fr.) A mineral 

 oil, rather thicker than tar, and of a 

 reddish-brown colour ; it has obtained its 

 name from the circumstance of its oozing 

 out of rocks like oil. In the East it is 

 burnt as oil. It is unctuous to the 

 touch, and exhales a strong and unplea- 

 sant odour. It is lighter than water, its 

 specific gravity being 87. In the island 

 of Zante, petroleum is at the present 

 time obtained from the same spot, and in 

 the same manner, as in the days of Hero- 

 dotus. The most powerful springs pro- 

 ducing petroleum are on the Irawaddi, in 

 the Burman empire. In one locality 

 there are said to be 520 wells, yielding 

 annually 400,000 hogsheads of petroleum. 

 It occurs in most countries where coal is 

 found. 



PETROSI'LEX. A fusible variety of horn- 

 stone ; according to some authors, the 

 same as clinkstone ; to others, compact 

 felspar. 



PETUN'TZE. The felspathe petuntze of 

 Brongniart. A variety of felspar, used 

 in the manufacture of porcelain. It is 

 called Petuntze by the Chinese. 



PE'TWORTH MA'RBLE. Called also Sussex 

 marble, occurs in layers varying from a 

 few inches to a foot and upwards in 

 thickness, separated from each other by 

 seams of clay. The Petworth or Sussex 

 marble is a limestone of various shades of 

 colour, occurring in the Weald clay ; it is 

 composed of the remains of fresh-water 

 univalves, shells of the paludina, and 

 crusts of the cypris faba, united into a 

 compact marble by a gangue of calcareous 

 cement. The more compact varieties 



bear a beautiful polish, and are elegantly 

 marked, when cut into slabs, by the sec- 

 tions of the contained shells. 



PHJENOGA'MOUS. (frpm 0aivw, to shew, 

 and y/iO, marriage, Gr.) The name 

 given to such plants as have the stamens 

 and ovarium distinctly visible. 



PHA'LANX. PI. Phalanges. (0o\ay, Gr. 

 phalange, Fr. falange, It.) The bones 

 composing the fingers and toes are termed 

 the phalanges. 



PHANEROGA'MIC. \ (from 0vEpo, mani- 



PHANEROGA'MOUS. $ fest, and ydfiog, 

 marriage, Gr.) Plants in which the sta- 

 mens and ovarium are distinctly visible ; 

 plants having the reproductive organs 

 visible. In all the phanerogamous plants 

 the whole of the double apparatus re- 

 quired for reproduction is contained in 

 the flower. The term is used in contra- 

 distinction to cryptogamous. 



PHARMA'COLITE. The name given by Bro- 

 chant to arseniate of lime. 



PHASIANF/LLA. (from phasianus, Lat. a 

 pheasant.) A genus of shells belonging 

 to the family Trochoida ; or, according 

 to Lamarck's arrangement, Turbinacea. 

 It is a solid ovate or conical univalve ; 

 opening longitudinal, ovate, and entire ; 

 lip thin ; columella smooth, with an at- 

 tenuated base. Recent phasianella? are 

 inhabitants of the Indian ocean, they are 

 found on the coasts and in estuaries, at 

 small depths only. These shells are 

 marked with beautiful lines of various 

 colours, and are much esteemed and 

 sought after for their beauty. 



Two species of Phasianella have been 

 found fossil at Grignon, P. turbinoides, 

 and P. semistriata. 



PHI'LLIPSITE. A mineral, found accom- 

 panying Herschelite. It is a species of 

 Harmotome or cross-stone, containing 

 lime and potash instead of baryta. 



PHO'LAS. (c&oAdg, from 0w\sw, Gr. to lie 

 concealed.) A genus of marine bivalves, 

 belonging to the family Inclusa ; or, ac- 

 cording to Lamarck's arrangement, the 

 family Pholadaria. A transverse gaping 

 shell, composed of two principal valves, 

 with several small accessory pieces placed 

 on the ligament or at the hinge. A long 

 curved tooth protrudes in each valve from 

 beneath the umbones. Pholades are 

 found at depths varying to nine fathoms ; 

 they pierce wood, rocks, indurated clay, 

 &c. They are much sought for in con- 

 sequence of their delicious flavour. The 

 history of none of the boring bivalves, 

 says Mr. Kirby, is more interesting than 

 that of the Pholads, or stone-borers. 

 These animals are defended by two very 

 fragile shells, strengthened indeed by sup- 

 plementary pieces, and rough like a file, 

 inhabited by a very soft animal which 



