PUN 



[373] 



P TT K 



sten have divided pumice into three 

 sub- species, namely, Glassy pumice, 

 Common pumice, and Porphyritic 

 pumice. Glassy pumice is dis- 

 tinguished from the other sub- 

 species by its darker colours, its 

 vitreous and conchoidal cross-frac- 

 ture, and its greater hardness and 

 translucency. Porphyritic pumice 

 is distinguished by its containing 

 crystals of felspar, quartz, and 

 mica, thus forming a sort of por- 

 phyry. Abich divides pumice into 

 two groups; the cellular being 

 dark green, poorer in silica and 

 richer in alumina, derived from 

 clinkstone, trachyte, or andesite; 

 the filamentous white, containing 

 more silica, and derived from tra- 

 chytic porphyry. Jukes. 



PU'NCTATED. (from pungo, Lat. to 

 prick.) Marked with small dots 

 or punctures ; full of small holes. 



PU'NCTTJLATED. Some of the ganoid 

 scales of Burdie House present 

 surfaces similarly punctulated. 

 Hugh Miller. 



PtfpA. ($upa t Lat.) 



1. In conch ology, a genus of cy- 

 lindrical univalve land shells, be- 

 longing to the family Colimacea. 



2. In entomology, the chrysalis; 

 one of the states of existence of 

 such insects as undergo metamor- 

 phoses. 



PU'RBECK BEDS. (The Calcaire Luma- 

 chelle Purbeckien of Brongniart.) 

 A fresh-water deposit, consisting 

 of various kinds of limestones and 

 marls. The Purbeck beds consti- 

 tute the lowest members of the 

 Wealden group, lying below the 

 Hastings sands, and immediately 

 above the Portland beds. The 

 Purbeck limestone abounds in or- 

 ganic remains, and the marble is 

 a congeries of small fresh-water 

 snail-shells (paludina), intermixed 

 with the minute crustaceous cover- 

 ings of a species of cypris. The 

 Purbeck beds consist of many thin 

 strata of argillaceous limestone, 



alternating with schistose marls, 

 and forming an aggregate of up- 

 wards of 300 feet in thickness. 



PU'RBECK STRATA. The lowest de- 

 posits of the Wealden group. 



PI/RPLE CO'PPER ORE. The Cuivre 

 pyriteux hepatique of Haiiy; the 

 buntkupfererz of Werner. A spe- 

 cies of sulphuret of copper. This 

 ore occurs in masses, or plates, or 

 disseminated; it is characterized by 

 its lively and variegated colours, 

 from which circumstance it is fre- 

 quently called variegated pyritous 

 copper. 



PU'RPURA. (purpura, Lat. the shell- 

 fish from which purple cometh.) 

 A genus of marine univalves be- 

 longing to the family Purpurifera. 

 The shells of this genus are found 

 at depths varying to twenty-five 

 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 notch- 

 ed, 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 numerous; 

 the animal secretes a purple liquor, 

 which was formerly used in dyeing. 

 Fossil and recent. 



PURPURI'FERA. A family of Tracho 

 lipoda in Lamarck's system, com- 

 prising the genera Buccinum, Gas- 

 sidarea, Cassis, Concholesas, Do- 

 Hum, Eburna, Harpa, Monoceros, 

 Purpura, Bicinula, and Terebra. 



PURPURO'IDEA. A genus of turbinated 

 and tubercolated univalves found 

 in the great oolite ; it is ventricose, 

 with one or more circles of spines 

 or tubercles : the aperture is large 

 ovate, the base widely notched, the 

 columella is smooth, rounded and 

 curves upwards at its base : three 

 species are found at Minchinhamp- 

 ton. Lycett. 



