PLATYCARCINUS. 



PLEODONTS. 



374 



of about 274 Ibs. Like iron, Platinum possesses the very valuable 

 property of welding at a high temperature, and this enables us to 

 form it into chemical vessels of great and daily use. 



The metals iridium, osmium, and palladium, occur in conjunction 

 with Platinum. 



Platin-Iridium consists of 76'8 Iridium and!9'64 Platinum, with some 

 palladium and copper. It is obtained at Nischnei Tagilsk, and also 

 at Ava in the East Indies. Another variety is found in Brazil. 



Iridosmine is a compound of Iridium and Osmium from the platinum 

 mines of Russia, South America, and the East Indies. Its composition 

 varies. One variety contains 



Iridium 46-8 



Osmium 49'3 



Rhodium 3'2 



Iron 0-7 



100 



Iridium and Rhodium are very hard, and are used as nibs for 

 gold pens. 



Native Palladium. Its form is supposed to be the regular octahe- 

 dron. It occurs mostly in grains, apparently composed of divergent 

 fibers. Colour steel-gray, inclining to silver-white. Ductile and 

 malleable. Hardness above 4'5. Specific gravity 11'8 12'2. This 

 ore consists of palladium, with some platinum and iridium. It fuses 

 with sulphur, but not alone. It is found in Brazil with gold, and is 

 distinguished from platinum, with which it is associated, by the 

 divergent structure of its grains. Selenpattadite is nothing but the 

 native palladium ; and Euyenesite is a similar compound. 



This metal is malleable, and when polished has a splendid steel-like 

 lustre which does not tarnish. A cup weighing 3$ Ibs. was made by 

 M. Breant in the mint at Paris, and is now in the Garde-Meuble of 

 the French crown. In hardness it is equal to fine steel. One part 

 fused with six of gold forms a white alloy ; and this compound was 

 employed, at the suggestion of Dr. Wollaston, for the graduated part 

 of the mural circle, constructed by Troughton for the Royal Observa- 

 tory at Greenwich. Palladium has been employed also for certain 

 surgical instruments. Large masses of the metal Palladium are 

 brought from Brazil. 



PLATYCA'RCINUS (Latreille), n genus of Crustacea. [CANCER.] 



PLATYCERCUS. [PSITTACID.E.] 



PLATYCRINI'TES. [ENCBINITES.] 



PLATYDA'CTYLUS. [GECKOTID.E.] 



PLATY'LEPAS. [CIBBIPEDIA.] 



PLATY'LOPHUS (Swainson), a sub-genus of Barita. [BABITA.] 



PLATY'MERA. [OXYSTOMA.] 



PLATYONYX, a genug of extinct Mammalia belonging to the 

 family Megatheriida. 



PLATYPEZID J5, a family of Insects belonging to the order Dijitera, 

 the sub-order Probotcidea, and the tribe Nemocera, 



PLATYPUS. [PBNITHORHYNCHUS.] 



PLATYRHOPALUS. [PACasroj!.] 



PLATYRHYNCHUS. [PHOCIDJS.] 



PLATYRHYNCHUS. [MCSCICAPIDJE.] 



PLATY'STERA. [MusciCAPiDJ!.] 



PLATYSTERNON. [CHEI.OXIA.] 



PLATY'STOMA and PLATY'STOMUS. [MrjsciCAPir).*;.] 



PLATYU'RUS. [STLVIAD*.] 



PLECO'TUS. [CHEIROPTERA.] 



PLECTEROPUS. [DOCKS.] 



PLECTOGNATHI. [FisH.] 



PLECTRANTHUS (from tKriicrpoi/, a cock's spur, and Mas, a 

 flower, in reference to the corolla being spurred or gibbous above the 

 base), a genus of Plants belonging to the natural order Labiatw. It 

 has a campanulate 5 toothed calyx in the floriferous state ; the teeth 

 equal or the upper one largest. The corolla with an exserted tube ; 

 the upper lip from 3-4-clft, the lower one entire, usually longer and 

 concave. There are 4 stamens, declinate, didynamous, the lower ones 

 longest ; free toothless filaments ; ovate uniform anthers. The species 

 are herbs, sub-shrubs, and shrubs. There are 45 species of this genus 

 described, which are of easy culture and propagation. 



P. crauifolitu is esteemed in India both as a perfume and a spice, 

 being equally valued in the toilet and the kitchen. The Patchouly, 

 so inimical to vermin and so efficacious in preserving cloths from moths, 

 is said to be the leaves of P. graveolens, which have a very powerful 

 odour, but the comminuted state in which it is imported renders this 

 uncertain. 



(Don, DiMamydeoiu Plants ; Burnett, Outlines of Botany.) 



PLECTR1S. [MELOLONTHID*.] 



PLECTRO'PHANES. [EMBKRIZIM:.] 



PLEIOCENE, or PLIOCENE. By this title (derived from *\t~ov, 

 more, and mtv6t, new) Sir Charles Lyell characterises the upper part 

 of the Tertiary Strata. There are in his view Older and Newer Pleiocene 

 Formations, and some have used for the latter class the expression 

 Pleistocene, or ' most new.' [TERTIARY SYSTEM.] 



PLEI'ODON. [NAIADACE*.] 



PLEI'ONE (Savigny), a genus of Dorsibranchiate (Amphirwme, 

 Blainv.) Annelida, which, with the same tentacles as Chloeia, Hav., 

 have branchiie in the form of tufts. The species are natives of tho 

 Indian seas, where some of them grow to a large size. 



PLEKOCHE'ILUS, the Rev. Lansdown Guilding's name for a genus 

 of Pupadce (Guild.), Btdimus of authors. 



Animal hermaphrodite. Body corrugate, heliciform ; head bilobate; 

 tentacles four, the two longer ones with oculiferous terminations; 

 mandible very lunate, the ossicula transverse, the triangular appendage 

 cutaneous. Intromittent organ retractile, at the root of the right 

 greater tentacle. Mantle perforated by a common' foramen. Ova few, 

 large, with a calcareous shell or crust. 



Shell barely umbilicate, dextral, oval, spiral ; the spire elevated, but 

 obtuse, the two last whorls largest, ventricose. Aperture entire, 

 elongated. Columella with a single plait, which is cavernoso-inflex. 

 Lip thickened, marginate. (Guild.) 



P. nm/ulatits has the body olivaceous-black, foot pallid beneath ; 

 tentacles white at the apex ; eyes black. The shell is stout, turgid, 

 plaited longitudinally, indistinctly striated transversely, ferruginous 

 chestnut, with oblique brown undulated bands ; whorls five. 



Plrknchdlvs unrlitlatti*, animal and shell. (Swainson, from Guildin&'R 

 drawing.) 



Shell of riejfoc?ieilus miditlatus. 



a, young; shell of same ; 6, egg magnified j e , natural size ; d, apex of nucleus, 

 enlarged. 



Mr. Guilding states that this fine species occurs in immense numbers 

 in the forests of the island of St. Vincent, generally withdrawn in the 

 daytime. The ova are agglutinated to the vaginating leaves of the 

 Tillandaia, which, from holding water, secure a damp atmosphere at 

 all times. 



PLEODONTS, the name assigned by Messrs. Dum<<ril and Bibron 

 to their first sub-family of Ldzards Lncertiens (Lacertian Lizards), or 

 Sauriens Autosaures (Autosaurian Saurians). 



The Pleodonts are divided into two great groups : the first with a 



