PLECANIUM. 



[ 606 ] 



PLEUROSIGMA. 



PLEC A 'NI UM, Reuss. Tertularia with 

 sandy sh'^ll-tissue come under this heading. 



BIIJL. Reuss, SitzHnqub. Wicn, xliv. 383. 



PLEOPELTIS, Humb. and Bonpl. An 

 exotic genus of Polypodieae (Polypodioid 

 Ferns), remarkable for the presence of 

 peculiarly formed so-called paraphyses in 

 the sori, performing- the function of an 

 indusium. These bodies are peltate, or 

 like minute flat mushrooms or umbrellas 

 expanded over and sheltering the sporanges 

 (tigs. 586, 587). 



Fig. 586. 



Fig. 587. 



Pleopeltis nuda. 



Fig. 586. A sorus, seen from above. 



Fig. 587. Vertical section of ditto. 



Magnified 25 diameters. 



PLEUROCAR'PI. MOSSES with late- 

 ral fruits. 



PLEUROCAR'PUS, Braun. A genus 

 of Zygnemaceae (Confervoid Aluee). 



2 species, in* freshwater pools. (Rabenh. 

 Alt/, iii. 258.) 



PLEUROCLA'DIA, Braun. A genus 

 of Fucoideoe, group Phaeosporeae. P. la- 

 cvstris\ freshwater. (Rabenh. Alg. iii. 393.) 



PLEUROCOC'CUS, Meneg. A genus 

 of Palmellaceae ( Unicellular Algae). 



Char. Cells single or collected in glo- 

 bular or cubical masses, globular or angular 

 from pressure, with a central nucleus; 

 cytioderm thick and hyaline ; cell-contents 

 homogeneous, green or reddish. Multipli- 

 cation by alternate fission in opposite direc- 

 tions. "Gonidia formed in special cells. 

 They present the greatest similarity to the 

 gonidia of Lichens. Several species = 

 forms of Protococcus ? 



BIBL. Meneg. Nostoch. 38 ; Na'geli, Syst. 

 124; Rabenh. Alg. iii. 24. 



PLEURODES'MIUM, Kiitz. An ob- 

 scure genus of Diatoiiiacese, allied to Stria- 

 teUa ; marine ; Africa. 



BIBL. Kiitz. Sp. Alg. 115. 



PLEUROM'ONAS', Perty. A genus of 

 Flagellate Infusoria. 



Char. Reniform, extremely delicate, 

 small, colourless; flagellum single, from 

 the concave side of the body, three times 

 its length. P. jaculans; motion jerking; 

 stagnant water. (Perty, Lebenxf. 171.) 



PLEURONE'MA, Duj. A genus of 

 Holotrichous Infusoria, family Colpodina. 



Char. Body oblong-oval, depressed, with 

 a broad lateral orifice, from which a bundle 

 of long, curved, floating and contiactile 

 ciliary filaments issue. 

 ^ P. "chrysalis, (crassa) D. (PL 31. fig. 66). 

 Freshwater. Other species. 



BIBL. Duj. Jnfifs. 473; Clap, et Lach. 

 Inf. 274 : Kent, Inf. 54i>. 



PLEUROPH'RVS, Clap. A genus of 

 Actinophryina (Rhizopoda). 



Char. Body invested with a sheath in- 

 crusted with extraneous siliceous particles. 



P. sphcerica. Freshwater. 



BIBL. Clap.etLachm. 7w/?/5.454; Archer, 

 Qu. Mic. Jn. 1870. 



PLEUROPYXTS, Corda. A genus of 

 Mucorini (Phycomycetotis Fungi), growing 



Fig. 588. 



Pleuropyxia microsperma. 

 Magnified 200 diameters. 



upon lejires and stems. This genus is im- 

 perfectly known. 



BIBL. Corda, Icon. Fung. pi. 6. fig. 291. 



PLEUROSIG'MA, Smith. A genus of 

 Diatomaceae. 



Char. Frustules single, free, longer than 

 broad ; front view linear or linear-lanceolate; 

 valves navicular, sigmoid, with a longitu- 



