PLOCAMIUM. 



[ 609 ] 



PODISOMA. 



from the last ; posterior brunch with three 

 set^, all arising from the last joint. 



r. unciiiatus. Beak curved upwards at 

 the end ; 3 sharp spines at anterior inferior 

 angrle of shell ; inferior antennae as the last. 

 P. hamaftts. Beak blunt and strong, 

 slightly curved downwards ; fir.st pair of 

 legs with a curved claw at the end. PMale 

 of P. trigonellus. 



BiBL. Baird, Brit. Entomostr. p. 134. 

 PLOCA'MIUM, Lamouroux. — A genus 

 of Delcsseriacese (Florideous Algte), con- 

 taining one species, P. cuccineum (PI. 4. 

 fig. 10), the commonest of our red sea- 

 weeds, with a delicate flat feathery thallus, 

 from '2 to 12" high, growing in bushy tufts 

 on rocks or other Algae. The fruit consists 

 of : — 1. coccidia, spherical, stalked or sessile 

 tubercles, at the sides or in the axils of the 

 ramules, tilled with angular spores ; 2. an- 

 theridia, which occur in inconspicuous flat 

 patches, composed of short erect cells, upon 

 the surface of distinct plants ; and 3. sti- 

 chidia, lateral or axillary, simple or branched 

 pods containing a single or double row of 

 linear (transversely parted) tetraspores. 



BiBL. Harvey, Mar. Alg. 19; Phyc. 

 Brit. pi. 44; GreV. Alg. Brit. pi. 12; Thuret, 

 Ann. Sc. Nat. 4 ser. iii. 19. 



PLCEO'TIA, Duj.— A genus of Infusoria, 

 family Thecamouadina. 



Char. Body diaphanous, with several 

 longitudinal ribs or keels in the middle, and 

 a rounded perfectly limpid margin. Two 

 anterior locomotive filaments, one flagelli- 

 lorm, the other trailii:g and capable of 

 arresting the movement of the body. 



P. vitrea (PI. 31. tig. 67). Marine; length 

 1-1200". Movement slow. 

 BiBi,. Duj. Infus. 34o. 

 PLffiSCO'NIA, B\i\., = Eiiphtes, Ehr. 

 PLUMATEL'LA, Lamk.— A genus of 

 freshwater Polyzoa, order Hippocrepia, 

 family Plumatellida?. 



Char. Zoary confervoid, branched, tubu- 

 lar, branches distinct ; tentacular disk cre- 

 scentic ; ova elliptical, with a marginal ring, 

 but no spines. 



P. repeiis. Zoary irregularly branched ; 

 cells subclavate, without a longitudinal fur- 

 row or keel ; tentacles about 60 ; tentacular 

 membrane dentate ; ova broad. 

 a. Adherent thrcugho'it. 

 /8. Attached only at the base. 

 P. fruticosa. Irregularly branched, at- 

 tached at the origin only ; cells cylindrical, 

 and destitute of furrow, but obscui-ely 

 keeled ; ova elongated. 



P. coraUoidcs. Attached at the base only ; 

 tubes dichotomous, densely tufted, desti- 

 tute of furrow and keel ; tentacles about 

 60 : ova broad. 



liiBL. AUman, Freshio. Pohjz. 92 ; Ann. 

 X. 11. 1844, xiii. 330; Johnston, Br. Zooph. 

 402; Parfltt, Ann. N. H. 1866, xviii. 171. 



PLU.AIULA'RIA, Lamk.— A genus of 

 Hydroid Zoophytes, family Plumulaiiidic. 



Char. Polypidom plant-like, rooted, sim- 

 ple, or branched, feathery ; cells small, uni- 

 lateral, usually seated in the axilla of a 

 horny spine ; egg-vesicles scattered. Ten 

 British species. 



P. cristata. Stem simple, a single tube, 

 pinnate; pinnae alternate; cells close, rim 

 toothed ; vesicles gibbous, girt with crested 

 ribs. 



P.falcata. Stem a single tube, -waved, 

 branched, branches alternately pinnate ; 

 cells close, shortly tubular, rim entire ; egg- 

 vesicles oval-oblong; common. 



In P. mgriophyllam & P. frutescens, the 

 stem consists of several parallel tubes. 



P. pinnuta, Linn. Stem a simple tube, 

 plumose; pinnae alternate, three on each 

 internode ; cells rather distant, campanulate, 

 appressed, rim entire ; vesicles pear-shaped, 

 rim toothed. 



P. setacea, Ellis. Stem a single tube, 

 pinnate ; pinuse alternate, one at each joint ; 

 joints ringed ; cells very remote, campanu- 

 late, rim even ; vesicles elliptical, smooth ; 

 common. 



BiBL. Johnston, Br. Zooph. 89; Hincks, 

 Hyd. Zooph. i. 294. 



■PLUMULARI'ID.E.— A family of Ily- 

 droida. 



BiBL. Hincks, Hijd. Zooph. i. 279, 



PODAXIXE'L— A family of Gastero- 

 mycetous Fungi, none of which are found 

 in Britain ; they are distinguished from all 

 allied tribes by a solid column in the centre 

 of the sporange. 



Many of the species grow on the hills of 

 the White Ant. 



BiBL. Montague, Ann. Sc. Nat. 2. xx. 

 69; Tulasne, Ann. Sc. Nat. 3. iv. 169; 

 Currev, Linn. Tr. xxvi. 288. 



PODISO'MA, Link.— A genus of Uredi- 

 nei (Hypodermous Fungi), growing upon 

 the living leaves and branches of species of 

 Juniper ; the filamentous mycelium creeping 

 beneath the epidermis, and sending up a 

 fleshy, stalk-like, tremelloid body (tig. 589), 

 composed of agglutinated tilaments (fig. 590) 

 terminating in bilocular spores (or two 

 spores adherent together), each of the cells 



2k 



