PUR 



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P Y R 



fathoms, and the greater number of the 

 species are littoral. The Purpura is an 

 ovate univalve, its surface being rather 

 rough with spines or tubercles ; aperture 

 notched, and slightly channelled in the 

 lower part ; the columella naked, flat, 

 depressed, and terminating in a point at 

 the base. The animal resembles that of a 

 true buccinum. The species are very nume- 

 rous ; the animal secretes a purple liquor, 

 which was formerly used in dyeing. Only 

 one species is described as having been 

 found fossil, namely, the purpura lapillus. 



PURPURI'FERA. A family of Trachelipoda 

 in Lamarck's system, comprising the 

 genera Buccinum, Cassidarea, Cassis, 

 Concholesas, Dolium, Eburna, Harpa, 

 Monoceros, Purpura, Ricinula, Terebra. 



PUTA'MEN. (put amen, Lat. a shell of a 

 nut.) In botany, another name for the 

 endocarp, stone, or shell of certain 

 fruits. 



PY'CNODONTS. (from TTVKVOQ, thick, and 

 odovQ, a tooth, Gr.) Thick-toothed 

 fishes. An extinct family of fishes 

 which prevailed extensively during the 

 middle ages of geological history. " Of 

 this extinct family," says Prof. Buck- 

 land, " there are five genera. Their 

 leading character consists in a peculiar 

 armature of all parts of the mouth with a 

 pavement of thick, round, and flat teeth, 

 the remains of which, under the name of 

 bufonites, occur most abundantly through- 

 out the oolite formation. 



PYCNO'DUS TRIGONUS. A genus of thick- 

 toothed fishes, belonging to the family of 

 Pycnodonts. 



PYCNI'TE. A mineral of a yellowish -white 

 colour, found principally at Altenberg, in 

 Saxony. 



PYRA'LLOLIT. A newly-discovered mine- 

 ral found in the lime quarries of Finland. 



PY'RAMID. (Trvpctfiig, Gr. from -n-vp, fire. 

 pyramide,r. pyramide, It.) The name 

 given to a certain figure, from its re- 

 sembling the shape of flame. A solid 

 figure, whose base is a polygon, and whose 

 sides are plain triangles, their several 

 points meeting in one. 



PYRA'MIDAL. ) Having the form of a py- 



PYRAMI'DICAL. 5 ramid. 



PYRAMIDE'LLA. A genus of marine uni- 

 valves, belonging to the family Plicacea. 

 It is found on coral reefs, sands, and 

 sandy mud, at depths varying to twelve 

 fathoms. The pyramidella is a turri- 

 culated univalve ; opening entire and 

 semi-oval ; columella projecting, with 

 three transverse folds, and perforated at 

 its end. 



PY'RENAITE. ) A greyish-black, dodecahe- 



PY'RENEITE. $ dral, opaque variety of 

 dodecahedral garnet. It consists of si- 

 lica 43, alumina 16, lime 20, oxide of 



iron 16, water 4. It is found in the 

 French Pyrenees, from which circum- 

 stance it has obtained its name, in lime- 

 stone. 



PY'RIFORM. (from pyrum, a pear, and 

 forma, form, Lat.) Pear-shaped; of the 

 form of a pear. 



PYRI'TES. (Trupi'rj/c, Gr. pyrites, Lat. 

 pyrite, Fr.) Sulphuret of iron. The fer- 

 sulfure of Haiiy, who has described six- 

 teen modifications of the primitive form 

 of its crystals. The colour of pyrites is 

 usually bronze yellow, passing to pale 

 brass yellow, and sometimes to brown. 

 It possesses the hardness of quartz, 

 striking fire with steel, and emitting an 

 odour of sulphur. Specific gravity from 

 4-10 to 4-80. Before the blow-pipe it 

 exhales a strong odour of sulphur, and 

 yields a brownish globule. It is com- 

 posed of sulphur and iron ; iron 47'85, 

 sulphur 52'15. It occurs in almost every 

 rock, stratified or unstratified. The 

 shining yellow streaks so common in our 

 coals afford familiar examples of pyrites. 

 It is a well-known property of iron py- 

 rites to decompose rapidly when laid in 

 heaps and moistened with water. There 

 are many varieties of pyrites, namely, 

 capillary, cellular, hepatic, radiated, &c. 

 &c. 



Mr. Webster gives the word pyrite, 

 making pyrites the plural, and he adduces 

 an authority in a quotation from Darwin ; 

 but it is most unusual to write pyrite, 

 and pyrites is used in the singular. 



PYRI'TOUS. Containing pyrites. 



PY'ROCHLORE. The pyrochlor of Werner. 

 Another name for octahedral titanium ore. 



PYRO'GENOUS. (from Trvp, fire, and ytwdu), 

 to produce, Gr.) Produced by fire, as 

 rocks of igneous origin. 



PYROLU'SITE. Another name for the com- 

 mon ore of manganese, as prismatic man- 

 ganese ore. 



PYRO'METER. (from Trvp, fire, and /zerpov, 

 measure, Gr.) An instrument for mea- 

 suring intense degrees of heat. The most 

 celebrated pyrometer is that invented by 

 Mr. Wedgewood, the extremity of his 

 scale reaching to 240 Wedgewood, or 

 32277 Fahrenheit. 



PYRO'METRY. The dilatation of bodies by 

 heat forms the subject of that branch of 

 science called pyrometry. There is no 

 body but is capable of being penetrated 

 by heat, though some with greater, others 

 with less rapidity ; and, being so pene- 

 trated, all bodies (with a very few ex- 

 ceptions, and those depending on very 

 peculiar circumstances), are dilated by it 

 in bulk, though with a great diversity in 

 the amount of dilatation produced by the 

 same degree of heat. 



PYRO'PE. (from Trvpo/Troc, Gr. pyropvs, 



