PONTOCYPRIS. 



[ 628 ] 



PORPHYRIDIUM. 



two species (PI. 34, fig. 23 a, scale of F. 

 rupee ; fig. 23 6, portion of wing, showing 

 tlie points of attachment of the two kinds 

 of scales). 



The scales may he separated by gently 

 pressing the nnder surface of the wings 

 against a slide. 



See Scales of Insects and Test-objects. 



BiBL. Westwood, Brit. Butterflies. 



PONTOCY'PRIS, Sars.— An Ostracode, 

 near Argillcccia among the Cypriclce, with 

 fragile pod-like yalves, higher in front than 

 behind ; no branchial appendage on the 

 second pair of jaws ; upper antennae long 

 and setiferous. 3 British species, rather 

 common. 



BiBL. Brady, Linn. Tr. sxvi. 384. 



POPPY.— The seeds of Poppies {Pa- 

 paver, L., Nat. Order Papaveraceoe) are ele- 

 gant opaque objects under a low power, the 

 testa being pitted so as to produce a reticu- 

 lated surface (PI. 39. fig. 14). 



PORCELLID'IUM, Glaus.— A genus of 

 Copepoda. 4 species, among Laminarics, 

 &c. (Brady, Copep., Ray Soc.) 



POKIF'ERA. See Spongida. 



POROCYC'LIA, Ehr.— A genus of Dia- 

 tomaceae closely allied to Liparogyba. 



BiBL. Pritchard, Infus. 823, 



PORODIS'OUS, Grev.— A genus of Dia- 

 tomacefe, fam. Melosirse. (Rabenht. Ah/, i. 

 85 ; Greville, Mic. Tr. 1863, 63 ; 1865, 46.) 



PORO'NIA, Fr.— A genus of Sphferiacei 

 (Ascomycetous Fungi), consisting of a corky 

 stroma, which is flat or hollowed out at the 

 top, and studded with the ostiola of the 

 perithecia. Tlie only British species is not 

 uncommon on horse-dung. 



BiBL. Fr. Si/st. Myc. ii. 330 ; Berk. Outl. 

 385; Cooke, Handb. 791; Tul. Carp. ii. 

 27, t. iii. 



POROSPH^'RA, Steinm.— Small glo- 

 bular fossils, common in the chalk, known 

 as OrhitoHn(T, formerly referred to Sponges 

 and Foraminifera, now found by Carter and 

 Steinmann to have Hydractinian structure ; 

 calcareous, with reticular tissue and radiate 

 tubes. (Steinmann, PaJceontoqraphica, 1878, 

 XXV. 120.) 



POROUS STRUCTURES of Plants. 

 — What are ordinarily called porous tissues 

 in vegetable anatomy are described in ac- 

 cordance with their real nature under the 

 head of Pitted structures. . True pores 

 do, however, occur in the walls of vegetable 

 cells, from secondary or ultimate changes in 

 their character. They are seen in the cells 

 of the leaves of Leucohryum and Spluiynum 



(see Sphagnace;e). Other regular orifices 

 are produced in the walls of the cells of 

 many of the zoospore-producing Confervoe, 

 as Conferva, Cladoplwra, Enteromorpha, &c. 

 (see PI. 9). The wall of the sporangial cell 

 of Achh/a presents analogous openings ; and 

 according to Cohn, pores are produced in 

 the spore-cells of SpHiEROPLEA to admit 

 the spermatozoids. The pits and the inter- 

 stices between reticulated fibrous secondary 

 deposits are often changed into true holes 

 in old cells, but this is the result of decay 

 of the primary membrane ; it takes place 

 very early however, at the contiguous ends 

 of SpiRAi.-fibrous and Pitted cells coa- 

 lescing to form ducts, changing the septum 

 formed by the adjoining ends into a kind of 

 grating, or irregularly torn diaphragm. 



PORPETA, Bail.— A genus of Diato- 

 macese, closely allied to Biddulphia. Gulf- 

 stream. 



BiBL, Pritchard, 7w/. 350 ; Rabenht. ^/^. 

 i. 315. 



POR'PHYRA, Ag.— A genus of Por- 

 phyraceae (Florideous Alg.Te), with an ex- 

 panded, membranous, shortly-stalked frond, 

 composed of a single layer of cells appi-oxi- 

 mated in fours, the contents purple or red. 

 Fructification consisting of: — 1. scattered 

 sori of oval spores ; 2. octospores immersed 

 in the frond ; and 3. antheridia, on the 

 same or distinct plants. P. laciniata and 

 vulgaris are common on our coasts. 



BiBL. Harvey, Mar. Aly. 261, pi. 25 A ; 

 Thuret, Ann. Sc. Nat. 4. iii. 5 ; Janczewski, 

 Mem. Soc. Cherhourq ., xvii. 345. 



PORPIIYRA'CE.E.— A tribe of Flori- 

 deous_ AlgfB (according to Thuret), of low 

 organization, forming Ulvoid membranous 

 fronds or strata of Confervoid filaments, of 

 a purple or red colour. They are ])laced 

 among the Ulvaceae by most authors, but 

 ditter in the absence of the zoospores and 

 the presence of tetraspores (octospores) and 

 antheridia. They are marine, — Porphyra 

 growing on rocks and stones, Banyin "the 

 same, or parasitic upon Zostera, Algae, &c. 



British Genera. 



Po}phyra. Frond plane, membranous, 

 very thin, of a purple colour, with oval 

 spores in sori, and tetraspores (square) 

 scattered all over the frond. 



Banyia. Frnnd filiform, tubular, com- 

 posed of numerous radiating cells in trans- 

 verse rows, enclosed within a continuous 

 hyaline sheaJi. 

 ■PORHPY RIDTUM = Palmella cruenta. 



