PERISTEPHANIA. 



[ '588 ] 



PETALOPUS. 



PERISTEPHA'NIA, Ehr. A genus of 

 Diatomaceae, closely allied to Stephana- 

 discus, differing, however, in having a 

 parallel (and non-radiate) arrangement of 

 the granules; and also to Systephania, 

 which differs only in having intramarginal 

 teeth. P. eutycha in deep Atlantic sound- 

 ings ; P. lineata in guano. 



BIBL. Pritchard, In/us. 824. 



PERITHE'CIUM. The name applied to 

 the special envelope, mostly of different 

 structure from the rest of the thallus or the 

 receptacle, enclosing the nucleus of the 

 Angiocarpous Lichens and the Pyrenomy- 

 cetous Fungi. 



PERITH'YRA, Ehr. A doubtful genus 

 of Diatomacese. Probably closely allied to 

 Coscinodiscus. 2 species from the Ganges. 



BIBL. Pritchard, In/us. 842. 



PERITRO'MUS, St. A doubtful genus 

 of Infusoria. (Kent, Inf. 759.) 



PERIZO'NIUM, Oohn et Jan. A genus 

 of Diatomaceae. 



Char. Frustules navicular, free, en- 

 circled with thick linear zones. 



P. Braunii (PI. 51. fig. 42), fresh- 

 water. 



BIBL. Rabenh. Alg. i. 228. 



PERO'NIUM, Cohn. A genus of Mona- 

 dina allied to Anthophysa. It is parasitic 

 on the spores of Pilularia, and consists of 

 a delicate, colourless fibre surmounted by a 

 globular head which resolves into numerous 

 narrow cells of a monadiform character. 



BIBL. Cohn, Entwick. 158 ; Pritchard, 

 Inf. 501. 



PERONOS'PORA, Ung. See BOTRYTIS, 

 & Smith, M. M. Jn. xvi. 120. 



PEROPH'ORA, Wiegm. A genus of 

 Tunicate Mollusca, family Clavelinidae. 



Char. Individuals stalked, roundish, com- 

 pressed ; thorax not marked with granular 

 lines. 



P. Listen. Occurs attached to sea- weeds. 

 Very transparent, appearing like little specks 

 of jelly dotted with orange and brown. 



BIBL. Forbes and Hanley, Br. Moll. i. 

 28. 



PERTUSA'RIA, DC. A genus of 

 Lichenaceous Lichens, having an adnate, 

 uniform thallus, spreading over bark, rocks, 

 &c., and bearing wart-like apothecia, finally 

 exhibiting a depressed pore in their centre, 

 leading to the one or several cells containing 

 the thecae. P. communis is very common 

 on trees. 



BIBL. Hook. Br. Fl. ii. pt. 1. 164; Engl. 

 Bot. pi. 677 ; Leighton, Lich. Flora, 226. 



PESTALOZ'ZIA, De Not A genus of 

 Melanconiei (Stylosporous Fungi), with 

 septate spores seated on a long pedicel, and 

 crested at the apex (fig. 711). Three species 

 occur in this country. P. Guepini is some- 

 times very destructive to Camellias. They 

 are beautiful microscopic objects. 



See fig. under STYLOSPOKES. 



BIBL. Berk. Outl. 324; Cooke, Handb. 

 471. 



PETALOM'ONAS, St. A genus of Fla- 

 gellate Infusoria. Free, ovate, depressed, 

 flagellum single, long, mouth at the ba.se 

 of the flagellum. 



P. abscissa = Cyclidium dbs., Duj.; other 

 species ; freshwater. (Stein, Inf. iii. : Kent, 

 Inf. 371.) 



PETALONE'MA, Berk. (Arthrosiplum, 

 Kiitz.). A genus of Oscillatoriacese (Con- 

 fervoid Algae), with a remarkable mode of 

 growth. The filaments are branched and 

 cylindrical, with an evident terete, gelatinous, 

 duplicate sheath (PI. 8. fig. 21). The inner 

 is thin and follows the filament; the outer 

 presents oblique striae indicating the inter- 

 position of lengths of the outer sheaths one 

 inside another, like a series of nested funnels 

 or conical cups. This appearance is pro- 

 duced by the bursting and expansion of 

 each length of the sheath at the apex alone, 

 to make room for the growth of the new 

 cells of the filaments formed at the apex. 

 This structure is analogous to that occurring 

 in UBOCOCCUS, where each parent-cell 

 membrane bursts at one side only to allow 

 the new one to emerge, thus at length 

 forming a jointed pedicel. The edges of the 

 funnels of Petalonema sometimes become de- 

 composed into curled filamentous processes. 



The filaments of P. alatum are green and 

 striated, about 1-3000" in diameter; the 

 inner sheath is yellowish, the outer colour- 

 less and 1-400" in diameter. It forms a 

 brownish stratum on rocks and stones. 



BIBL. Berkeley, Gleanings, 23, pi. 7 ; 

 Greville, Crypl. Fl. pi. 222; Hassall, Fr. 

 Alg. 237, pi. 68 ; Kiitz. Spec. Alg. 311 ; Tab. 

 Phyc. ii. 28 ; Al. Braun, Rejuven., Ray Soc. 

 1853, 178 ; Rabeiih. Alg. ii. 265. 



PETALOPHYL'LUM, Wilson. A ge- 

 nus of Pellieaa (frondoso Hepaticae). P. 

 Ralfsii is an elegant little Liverwort with 

 the* frond plaited or lamellated in rays from 

 the origin of the fruit. 



BIBL. Engl. Bot. Supp. pi. 2874. 



PETAL'OPUS, Clap, et Lach. A genus 

 of Amoebaea (Rhizopoda). Pseudopodia 

 filiform, arising from one point of the sur- 



