PLAGIODISCUS. 



[ 604 ] 



PLANARIOLA. 



Fig. 585. 



plants of the family, its stems gi'owing from 

 3 to 5" long. 



BiBL. Hook. Br. Fl. ii. 

 pt. 1, 111 ; Br. Jung. 

 pis. 13, 14 ; Ekart, >S>h- 

 ops. Jung. 6 et seq, pi. 1 ; 

 Endlicher, Gen. Plant. 

 Supp. 1, No. 473. 



PLAGIODIS'CUS,Gr. 

 — A gemis of Diatoma- 

 cese. Allied to Surirella, 

 but the costae radiating 

 at the ends. 2 species ; 

 valves reniform ; Hondu- 

 ras. (Grunow, M. M. Jn. 

 xviii. 172, figs.) 



PLAGIOG'NATH.1, 

 Duj. — A genus of Rota- 

 toria containing- species ^it%t^„U^|fait. 

 included by Enrenberg 

 in the genera Notommata, Diglena, and 

 Distemma ; distinguished by the arched 

 back and peculiar jaws. 



BiBL. Duj. Inf. 651; Pritchard, Itif. 

 692. 



PLAGIOGRAM'MA, Grev.— A genus 

 of Diatom acese, family Fragilarife. 



Char. Frustules quadrangular, united into 

 a short fascia; valves with two or more 

 sti'ong, pervious transverse costre, and mo- 

 niliform generally interrupted strise. 



BiBL. Greville, Mic. Tr. 1865, 1866; 

 Rabenh. Fl. Eur. Alg. i. 117 ; Pritchard, 

 Infus. 778. 



PLAGIOPH'RYS, Clap.— A genus of 

 Actinophryina (Rhizopoda). 



Char. No carapace, pseudopodia nume- 

 rous, arising from one point of the surface 

 of the body. 2 species ; fi-esh water. P. cy- 

 lindrica (PI. 52. tig. 17). 



BiBL. Clap, et Lach. Infus. 453 ; Archer, 

 Qu. Mic. Jn. 1871, 146. 



PLAGIOPOGON, St.— A genus of Ho- 

 lotrichous Infusoria. Free, oval, longitudi- 

 nally furrowed, oral setee rigid. P. cohps ; 

 length 1-300". (Kent, /«/. 508.)  



PLAGIOP' YLA, Stein.— A genus of Ho- 

 lotrichous Infusoria. Ovate ; mouth ven- 

 tral, with an undulating membrane ; sur- 

 face with trichocysts. 3 species ; fresh and 

 salt water. (Kent, Inf. 538.) 



PLAGIOT'OMA, Duj.— A genus of Bur- 

 sarina (Infusoria ciliata). 



Parasitic ; in the intestines and their walls 

 of Vertebrata and luvertebrata, and in the 

 mucus of Mollusca. 7 species. P. lumbrici^ 

 in the earthworm j P, coli, in the human in- 

 testine. 



Clap, et Lach. 



A genus of 



BiBL. Duj. Inf. 504 

 Infus. 235. 

 PLAGIOTRICHA, Kt 



Hypotrichous Infusoria : allied to Oxgtncha 

 2 species; freshwater. (Kent, Inf. 771.) 



PLAGIOT'ROPIS, O'Meara.— A genus 

 of Diatomaceae closely allied to Amphi- 

 prora, Ehr. 



BiBL. O'Meara, Qu. Mic. Jn. 1874, 88. 



PLANA'RIA, MiilL— A genus of Annu- 

 loida, of the order Turbellaria, and sub- 

 order Planarida. 



Char. Body soft, flattened, oblong or 

 oval, not jointed, covered with vibratile 

 cilia ; neither suckers, bristles, nor leg-like 

 appendages present. 



Some parts of the structure of these ani- 

 mals have been noticed under Annul at a 

 in speaking of the Turbellaria. The mouth 

 is situated on the under sm-face of the 

 middle of the body, at the end of a retrac- 

 tile proboscis ; there is no anus ; the mouth 

 leads to a capacious stomach giving ofl 

 dendritically-branched caeca, somewhat as 

 in one joint of a Tcenia (PI. 21. fig. 14). 

 Their motion is continuous and gUding, 

 upon water-plants, or the sides of glass jars. 

 The anterior part of the body exhibits a 

 curved row or a single pair of eyes, and 

 sometimes ear-like projections. They mul- 

 tiply by division, and the formation of ova, 

 which are enclosed in a coloured capsule. 



Some of the species are very common in 

 pools, and resemble, at first sight, minute 

 leeches. P. nigra, which is black, has a 

 row of marginal anterior eyes, and two 

 lateral and one mesial projection ; length 

 about 1-2". P. hrunnea, dusky-brown, with 

 a dark mesial line ; eyes as above ; length 

 rather less. P. lactea, cream-coloured, 

 tinged with pale reddish brown, truncate in 

 front, Avith two slight lateral auricles ; eyes 

 two or foiu- ; length 1-2 to 3-4". P. torva., 

 grey or black : obtu.-e in front, angles 

 rounded, centre proj ecting ; eyes two, with 

 a white halo ; length 1-2". Of the other 

 species some are marine. 



BiBL. Johnston, Non-parasitical Worms ; 

 Duges, Ann. Sc. Nat. 2. xv. and xxi. ; 

 ffirsted. System, d. Plattioiirmer ; Diesing, 

 Helminth. ; Daly ell. Powers of Creation, ii. ; 

 Schultze, Naturg. TwhelL ; J luxley, Cofnp. 

 An. ; Vaillant, Mn. Mic. Jn. i. 311 ; R. 

 Lankester, Pop. Sc. Rev. 1867, vi. 388 ; 

 Moseley, Phil. Trans. 1877, xvii. lOo. 



PLANARI'OLA, Duj.— A doubtful ge- 

 nus of Infusoria. 



P. rubra (PI. 31. fig. 65). Aquatic, in 



