ARTHONIA. 255 



On shady rocks near the ground, in various parts of Eng- 

 land and Ireland ; not common. 



Genus VIII. ARTHONIA, Ach. 

 Gen. Char. Apothecium roundish or difformed, tumid, innately 

 sessile, covered with a subcartilaginous membrane, within subge- 

 latinous. Perithecium none. Thalamium nearly plane, not bor- 

 dered, black, rough. Thallus cartilaginous-membranaceous. (Name 

 from ap0a), or properly a/oSa>, to sprinkle, in allusion to the apo- 

 thecia (hence called ArdeUce), resembling spots sprinkled over the 

 thallus.) 



1. Arthonia astroidea {aarpovj a star). Thallus thin, 

 membranaceous, smooth, scaly, white, cream-coloured or 

 olive, limited ; ardellse innate, clustered, substellate or radiate. 

 Thalamium blackish, plane, rough. Spores linear-clavate, 

 rounded at ends, triseptate. (E. B. 1847.) 



Common on the smooth bark of forest-trees. 



2. Arthonia Swartziana. Ardellse subsessile, clustered 

 into irregular angular or subradiate shapes ; thalamium 

 black, plane, cracked. Spores broadly obovate, triseptate. 

 (E. B. 2079.) 



Common on the smooth bark of the ash and other forest- 

 trees. 



