Rev. W. A. Leighton on the British Graphidese. 437 



oblong, simple or branched ; disk dark brown, plane, roughish ; 

 sporidia linear-clavate, 3-septate. 



Graphis microscopica, Ehrhart, Cnpt. 273 (1791 ?)• 



Opegrapha epipasta, ^. caragancc, Ach. Metli. 26 (1803); L. Univ. 258. 



Opegrapha microscopica, Sm. E. Bot. 1. 1911 (1808). 



epipasta, p. microscopica, Ach. Syn. 75 (1814); Hook. Br. Fl. 2. 144. 



Arthonia microscopica, ». stenograpta, Wallr. Crypt. Germ. 322 (excl. some 

 syn.). 



On young oaks and alder. Sussex ! Mr. Borrer. 

 Thallus forming irregular transverse patches on the smooth 

 bark of trees of a transversely oblong or elongated shape, well- 

 defined by its colour, but not bounded by any dark line, very 

 thin, smooth, somewhat shining, varying fi-om pale greyish-yellow 

 to a greyish-olive or even copper-colour. Ardella tolerably nu- 

 merous, distantly scattered over the thallus in a parallel trans- 

 verse direction, veiy variable in shape and size, minute and 

 roundish or oval, or larger oblong or elongato-oblong, obtuse 

 and rounded at the extremities, innate, but slightly raised above 

 the surface, mostly simple, in a young state covered by the 

 thallus which is ruptured by the emergence of the lirella, and is 

 then apparently thrown back so as to form a sort of spurious 

 tballodal margin closely appressed along the sides of the lirella. 

 Disk dark brown, plane and open, tumid and convex when 

 wetted, roughish, surrounded by what appears as a veiy slender 

 black proper margin always visible, especially so in those ardellce 

 whose disk has been abraded, but when carefully examined 

 found to be illusory, arising in reality from the black surfa(« 

 of the disk bending over the sides of the ardella and inserting 

 itself under the membranous tballodal margin, which is in 

 consequence somewhat thickened and upraised, and appears 

 darker as a very narrow margin to the disk. The vertical sec- 

 tion shows this structure, and also that of the nucleus which is 

 gelatinous and hyaline, having imbedded in it in regular arrange- 

 ment roundish-clavate asci, each containing eight sporidia of a 

 linear-clavate form, 3-septate ; the whole covered externally and 

 laterally by the dark subpulveruleut matter constituting the 

 disk. Tliere is no trace of any carbonaceous, horny or even 

 membranous receptacle in the ardella. ' 



Not to be confounded with Verrucaria punctiformis and Ver- 

 rucaria epidermidis, /3. analepta, which are very frequently found 

 growing side by side with it on the same bark. 



The specimens of Opeg. epipasta in i\Ir. Borrer's herbarium 

 were in too imperfect a state to determine anything accurately 

 concerning them. They were however evidently belonging to 

 the genus Arthonia, 



Plate VII. fig. 30. a. Vertical section of thallus and ardella ; h, sporidium ; 

 c, asci imbedded in the nucleus. 



