PSOROPTES. 



[ 541 ] 



PTERODINA. 



copodiacese), remarkable for their trilocular 

 capsules and minute leaves (fig. 616). 



Fig. 616. 



Fragment of a branch of Psilotum triquetrum. 

 Magnified 10 diameters. 



PSOROPTES (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 other mam- 

 malia?). 



P. equi (PL 2. fig. 18), itch-insect of the 

 horse. Found upon the scaly crusts formed 

 upon the body. Mandibles each terminated 

 by two teeth, and not chelate ; palpi three- 

 jointed, and adherent to the labium; ventral 

 surface covered with parallel, undulating 

 rugae ; at the end of the body are two fleshy 

 lobes terminated by a tuft of setae. 



BIBL. Hering, Nov. Act. n. cur. xviii. 

 585; Gervais, Walckenaer's Apteres, iii. 266; 

 Dujardin, Obs. au Micr. 147. 



PSOROSPERMLE. These bodies were 

 discovered by J. Miiller, and appear to re- 

 present the pseudo-naviculae of the Grega- 

 rinee of fishes. 



They are microscopic, oval, depressed, or 

 discoida! corpuscles, with or without a tail, 

 exhibiting no movements, and consisting 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 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 im- 

 bedded 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". 



BIBL. Miiller, Archw, 1841.477, 1842. 

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

 Helminthes, 643; Leydig, Mull. Archiv, 

 1851. 221 (Microsc. Journ. 1853. i. 206); 

 C. Robin, Vegetaux parasitiques, fyc., 2 ed. 

 p. 291. 



PTERIDE^E. A subtribe of Polypoda> 

 ous Ferns, with indusiate sori. 



Synopsis of the Genera. 



I. PTERIS. Sorus marginal, linear, con- 

 tinuous. Indusium marginal, linear, free 

 within. Veins pinnate. 



II. LITHOBROCHYA. Sorus marginal, 

 linear, continuous. Indusium marginal, 

 linear, free within. Veins anastomosing in 

 hexagonoid spots. 



III. AMPHIBLISTRA. Sorus marginal, 

 linear, continuous. Indusium marginal, li- 

 near, free within. Veins very much branched 

 with free venules. 



IV. BLECHNUM. Sori inserted on trans- 

 verse venules connecting the veins, conti- 

 guous or continuous by confluence, parallel 

 with the rib, and more or less approximated. 

 Indusium linear, the free margin looking 

 towards the rib. Veins pinnate, anasto- 

 mosing. 



PTERIS, Linn. A genus of Pteridea? 

 (Polypodaeous Ferns), represented by one 

 indigenous species, Pteris aquilina, common 

 Brake Fern. 



Fig. 617. 



Pteris. 



A pinnule with marginal indusiate sori. 

 Magnified 10 diameters. 



PTERODINA, Ehr. A genus of Rota- 

 toria, of the family Brachionaea. 



Char. Eyes two, frontal ; foot simply sty- 

 liform. At the end of the tail-like foot is a 

 suctorial disk; jaws with the teeth either 

 arranged in a row, or two teeth only in each. 



Three species; two aquatic, one marine. 



