PSILOTE/E. 



[ 043 ] 



PTEiaUE^E, 



Tmesipferis. Sporanpfes sessile, three- 

 celled, buvsting iiiipovfectlv into two v<alves 

 by a vertical crack, lillcd with nioaly spores. 

 ' Isoetes. Sporani>-es imbedded in the bases 

 of the leaves, and adnate at the back, not 

 valvate, with sevenil transverse septa ; con- 

 taining two kinds of spores (iu distinct spo- 

 rangia). 



Fig. 610, 



Pbilotum iriquftium. 

 Nat. size. 



Fig, Gil. 



Fragment of a branch of Fsilotum triqui'trum. 

 Magnified 10 diameters. 



PSILOT'RICIIA, St,— A genus of ITy- 

 potrichous Infusoria. Bodyoblong, flattened, 

 with 2 rows of long ventral, and a peripheral 

 row of setae, but no styles. P. acuminata, 

 freshwater. (Kent, Inf. (572.) 



PSILO'TUM, Swartz. {Lycopodium nu- 

 dum, Ij. ). — An exotic genus of P.'^iloteaj (Ly- 

 copodiaceoe), remarkable for their trilocular 

 capsules and minute leaves (fig. 611 ). 



PSORO'MA, Nyl.— A genus of Lichena- 

 ceous Lichens, with large distinct gonidia. 



BiBL. Leighton, Lick. Flora, 14'J. 



PSOROP'TES, Gervais.— A genus of 

 Arachnida, of the order Acarina, and family 

 Acarea. 



Char. Body soft, depre.«sed, with rigid 

 hairs beneath, and on the legs. 



Parasitic upon the horse and sheep, and 

 the ox. 



P. equi (PL 6. fig. 18), itch-insect of the 

 horse. Found upon the scaly crusts formed 

 upon the body. Mandibles elongate, didac- 

 tyle, each terminated by two teeth; palpi 

 three-jointed, and adherent to the labium; 

 ventral surface covered with parallel undu- 

 lating rugae ; at the end of the body are 

 two fleshy lobes, terminated by a tuft of setae, 



BiBL. 'Hering, Nov. Act. xviii. 585; Ger- 

 vais, Walclienners Aptcres, iii. 266; Dujar- 

 din, Micr. 147 ; Murray, Ec. Ent. 307 ; 

 Megnin, Paras. 189. 



PSOROSPERMI^.— These bodies were 

 discovered by Miiller, and appear to repre- 

 sent the pseudo-naviculaj of the Greyarinm 

 of fishes. 



They are microscopic, oval, depressed, or 

 di.scoidal corpuscles, with or without a tail, 

 exhibiting no movements, and con.si.stiug of 

 a tolerably firm outer coat, containing one 

 or two oblong contiguous vesicles at that 

 end of the body opposite the tail. They are 

 about 1-2500 to J -2000" in length, and are 

 contained in immense numbers in minute 

 cysts, in almost every part of the body of 

 fishes, as upon the gills, in the muscles, and 

 between the coats of the eye, in the swim- 

 ming-bladder, &c. Sometimes they are 

 imbedded in a ramified sarcodic mass. 



Diameter of the cysts on the pike 1-50 to 

 1-25" ; of the corpuscles, length 1-2000", 

 breadth 1-3500". See Pebrine. 



BiBL. Muller, Archiv, 1841. 477, 1842, 

 193; Creplin, ibid. 1842. 61; Dujardin, 

 Helminthes, 643; Leydig, Mi'dl. Archiv, 

 1851, 221, Mic. Jn. 1853, i, 200; Robin, 

 Ve(jet. Parasit. 2. 291. 



PTERID'E^.— A family of Polypodia- 

 ceous F.ems. Genera: 



2x2 



