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C 213 } 



PUR 



and, in all probability, served the purpose 

 of supporting some membrane which en- 

 abled the animal to fly. The fingers ter- 

 minated in long hooks, like the curved 

 claws of the bat. The form and size of 

 the foot, leg, and thigh, show that this 

 extraordinary animal was capable either 

 of standing firmly on the ground, or of 

 perching upon the branches of trees. It 

 is deemed probable that the pterodactyle 

 had the power of swimming. 

 PTE'ROPODS. ) (from Trrepov, a wing, and 

 PTERO'PODA. S Trovf, a foot, Gr.) A 

 class of molluses possessing organs adapt- 

 ed for either swimming or sailing. The 

 genera belonging to this class have the 

 sac formed by the mantle closed on every 

 side ; a structure rendering it necessary 

 that the gills should be placed externally, 

 as regards the sac; and they are found 

 spreading out like a pair of wings on each 

 side of the neck. This position of the 

 gills, causing them to resemble the wings 

 of an insect, suggested to Cuvier the name 

 which he assigned to the class. Four ge- 

 nera only are known, namely, Clio, Cym- 

 bulia, Pneumodermon, and Limacina. 

 These molluscs abound in the colder re- 

 gions of the ocean, and the clio borealis 

 is considered to form the chief source of 

 food for the whale. 

 PTERO'PODOUS. Belonging to the class 



Pteropoda ; wing-footed. 

 PUBE'SCENCE. (from pubesco, Lat. to grow 

 mossy, or hairy. ) The downy substance 

 on plants, resembling fine silken short 

 hairs. 

 PUBE'SCENT. Clothed with fine hairs or 



down. 



PU'DDING-STONE. A conglomerate com- 

 posed of rounded stones imbedded in a 

 paste. Pudding-stone is distinguished 

 from breccia by the form of the contained 

 pebbles : in the latter they are sharp an- 

 gular fragments ; in the former they are 

 rounded nodules. 



PULVINI'TES. (from pulvinus, Lat. a 

 cushion.) A fossil bivalve found in the 

 baculite limestone of Normandy. 

 PU'MICE. ^ (pumex, ~L&t.pomice, It.) 



PU'MICE STONE. \ A light, spongy, fibrous 

 lava, produced by the action of gases on 

 trachytic and other lavas. The island of 

 Lipari contains a mountain entirely form- 

 ed of white pumice : when viewed from a 

 distance, the appearance is that of a moun- 

 tain completely covered with snow. Pumice 

 is supposed to have been produced from a 

 considerable disengagement of gas, while 

 the lava was in a plastic, but not in a fluid 

 state ; the escape of the gas producing the 

 porous structure which characterizes pu- 

 mice stone. Pumice is very light, and swims 

 upon water, its specific gravity being 

 about 9*0. It is fusible before the blow- 



pipe, melting into a whitish enamel or 

 glass. Klaproth gives the analysis of a 

 specimen from Lipari as follows : silex 

 76*5, alumine 17*5, soda and potash 5-0, 

 iron 1'75. Immense quantities of pumice 

 are sometimes ejected from volcanoes. 



PUMI'CEOUS. Having the characters of 

 pumice ; resembling pumice ; containing 

 pumice. 



PU'NCTATED. (from jtmw^o, Lat. to prick.) 

 Marked with small dots or punctures ; 

 full of small holes. 



PU'PA. (pupa, Lat.) 



1. In conchology, a genus of cylindrical 

 univalve land shells, belonging to the 

 family Colimacea. 



2. In entomology, the chrysalis ; one of the 

 states of existence of such insects as un- 

 dergo metamorphoses. The insect in its 

 pupa state of existence appears as if wrapt 

 in a shroud, presenting no appearance of 

 external members, and retaining but 

 feeble indications of life. In this con- 

 dition it remains for a certain period, 

 until the time arrives when it is quali- 

 fied to emerge into the world, by bursting 

 asunder the fetters which had confined it, 

 and to commence a new existence. 



PU'RBECK BEDS. A fresh-water deposit, 

 consisting of various kinds of limestones 

 and marls. The Purbeck beds constitute 

 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 con- 

 geries of small fresh-water snail-shells 

 (paludina), intermixed with the minute 

 crustaceous coverings of a species of 

 cypris. Dr. Mantell. 



PU'RBECK STRATA. The lowest deposits 

 of the Wealden group. 



PU'RPLE CO'PPER ORE. The Cuivre py- 

 riteux hepatique of Haiiy ; the buntkup- 

 fererz of Werner. A species 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 frequently called 

 variegated pyritous copper. It has a 

 metallic lustre ; fracture conchoidal, with 

 small cavities. Specific gravity from 

 4'95 to 5-46. It effervesces with nitric 

 acid, imparting to it a green tinge. Be- 

 fore the blow-pipe, on charcoal, it melts, 

 yielding a metallic globule. According 

 to Klaproth, its constituents are, copper 

 58, iron 18, sulphur 19, oxygen 5. It 

 occurs in metallic veins, and in beds, most 

 commonly in primary rocks. 



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

 from which purple cometh.) A genus of 

 marine univalves belonging to the family 

 Purpurifera. The shells of this genus are 

 found at depths varying to twenty-five 



