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



2. Arthonia punctiformis, Ach,, «. olivacea, Ach. Thallus 

 thin, membranous, smooth, shining, copper- coloured, indeter- 

 minate ; ardellse subinnate, scattered, roundish or broadly ob- 

 long, simple ; disk dark brown, plane or slightly convex, rough ; 

 sporidia linear-clavate, obtusely pointed, 3-septate. 



Arthonia punctiformis, a. olivacea, Ach. L. Univ. 141 (1810) j Syn. 4; 



Mart. Fl. Erlang. 283; Sommerf. Suppl. Lapp. 141. 

 Opegrapha punctiformis, Fingerh. EifH. 25(1829). 



On young oaks. Sussex ! Mr. Borrer. 



Thallus very thin, smooth, even and shining, somewhat scaly, 

 pale brown or darkish copper-colour, forming irregular indeter- 

 minate patches. Ardella few, distantly scattered, larger than in 

 the last, variable in size and shape, roundish or broadly oblong, 

 simple, slightly raised above the surface, probably in a young 

 state covered by the thallus, which in a later stage is cracked 

 around the ardella, forming an inconspicuous spurious thallodal 

 margin. Disk dark brown, plane or slightly convex, coarsely 

 roughened by raised points or minute tubercles, which a vertical 

 section shows to be thinner portions of the dark external disk, 

 towards which the asci, which seem collected into sets, converge, 

 and through which the spoi'idia are probably ultimately ejected. 

 This peculiarity of structure I have not noticed in any other 

 species. Nucleus gelatinous and hyaline, with broad rounded 

 asci imbedded, each with eight pale yellow sporidia of a linear- 

 clavate or obovate form, obtusely pointed at the extremities. 

 3-septate, covered externally by a darker layer constituting the 

 disk. 



Acharius doubts whether 'his Opegrapha epipasta /3. micro- 

 scopica n)ay not be a form of his Arthonia punctiformis, but I 

 incline to think them distinct. 



(3. galactina, Ach. Thallus pale yellow or cream-colour. — Ach. 

 L. Univ. 141 ; Syn. 4. 



On young oaks. Sussex ! Mr. Borrer. 



In all other respects, except the colour of the thallus, similar 

 to var. a. 



Plate VII. fig. 31. a, Vertical section of thallus and ardella; b, sporidia. 



3. Arthonia astroidea. Thallus thin, membranous, smooth, 

 scaly, white, cream- colour, or olive, limited; ardellse innate, 

 clustered, substellate or radiate; disk blackish, plane, rough; 

 sporidia in asci, eight, linear-clavate, rounded at the extremities, 

 3-septate. 



Opegrapha radiata, Pers. in Ust. Ann. st. 7- p- 29. t. 2. f. 3. B. b. (1794). 



Lichen astroites, Ach. Prodr. 24 (1798). 



Opegrapha astroidea, Ach. Meth. 25 (1803); Sm. E. Bot. t. 1847. 



