PSILOTE.E. 



[ 043 



PTERIDEJ3. 



Tmesipteria. Sporanges sessile, three- 

 celled, bursting imperfectly into two valves 

 by a vertical crack, tilled with mealy spores. 

 " Isoetfs. Sporanges imbedded in the bases 

 of the leaves, and adnate at the back, not 

 valvate, with several transverse septa ; con- 

 taining two kinds of spores (in distinct spo- 

 rangia). 



Fig. 610. 



Psilotum triquetrum. 

 Nat. size. 



Fig. 611. 



Fragment of a branch of Psilotum triquetrum. 

 Miigniflcd 10 diameters. 



PSILOT'RICIIA, St. A genus of lly- 

 potrichous Infusoria. Body oblong, tlatu-ncd, 

 with 2 rows of long ventral, and a peripheral 

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

 freshwater. (Kent, Inf. 672.) 



PSILOTUM, Swartz. (Lycopodium n- 

 dum, L.). An exotic genus of Pailotese (Ly- 

 copodiacere), remarkable for their trilocular 

 capsules and minute leaves (tig. 611). 



PSORO'MA, Nyl. A genus of Lichena- 

 ceous Lichens, with large distinct gonidia. 



BIBL. Leighton, Lich. Flora, 14',). 



PSOROP'TES, Gervais. A genus of 

 Arachnida, of the order Acarina, and family 

 Acarea. 



Char. Body soft, depressed, with rigid 

 hairs beneath, and on the legs. 



Parasitic upon the horse and sheep, and 

 the ox. 



P. equi (PI. 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 setse. 



BIBL. Heriug, Nov. Act. xviii. 585; Ger- 

 vais, Walckenaer^s Apttres, iii. 266 ; Uujar- 

 diu, Micr. 147; Murray, EC. Ent. 307; 

 Me'gnin, Paras. 189. 



PSOROSPERMLE. These bodies were 

 discovered by Mu'ller, and appear to repre- 

 sent the pseudo-navicula3 of the Gregarince 

 of fishes. 



They are microscopic, oval, depressed, or 

 discoidal corpuscles, with or without a tail, 

 exhibiting no movements, and consisting of 

 a tolerablv firm outer coat, containing one 

 or two oolong contiguous vesicles at that 

 end of the body opposite the tail. They are 

 about 1-2500 to 1-2000" 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 PEBRINB. 



BIBL. Miiller, Archtv, 1841. 477, 1842. 

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

 Helminthes, 643; Leydig, Mutt. Archiv, 

 1851, 221, Mic. Jn. 1853, i. 206; Robin, 

 Vtgtt. Parasit. 2. 291. 



PTERID'E^. A family of Polypodia- 

 ceous Ferns. Genera : 



2x2 



