100 CRYPTOGAMIA LICHENES. 



2. O. atra, crust membranaceous, white ; apothecia sessile, li- 

 near, flexuose, free, channelled along the middle SCH^ERER. O, 

 denigrata, SMITH in Eng. Sot. (ARNOTT in Litt.) 



Hab. On the bark of various trees, particularly the hazel 

 and the ash, very common. 



For the specific character, which is a translation of SCH^ERER'S, 

 I am indebted to Mr ARNOTT, who also determined my 

 specimens. The crust is thin, even, smooth, silvery white, 

 undefined, except when it comes in contact with another 

 frond, when the point of separation is marked by a black 

 line. The apothecia are black, raised, variable in length, 

 mostly simple, but occasionally branched, numerous, free, 

 or somewhat clustered, and slightly tapered at each end. 

 The disk is rather narrow. Notwithstanding its common- 

 ness, this is the first time it has been described as a native 

 of Scotland. 



3. O. notha, crust very thin, spreading, greyish-white ; apothe- 

 cia scattered, black, short, oblong, with a broad disk, GREV. Fl. 

 Edin. 352. Eng. Sot. t. 1890. 



Hab. On the bark of the ash, not common. 



4. O. scripta, crust spreading, thin, smooth, greyish-white ; apo- 

 thecia black, immersed, flexuose, anastomosing or somewhat stel- 

 late. GREV. FL Edin. 353, t. iii. f. 3. indifferent. Graphis scripta, 

 HOOK. Scot, ii, 43. 



Hab. Bark of trees, particularly of hazel, frequent. 



The apothecia burst through the crust, leaving the margins 

 a little raised, and uneven or lacerate. The Lichen scrip- 

 tus of LIGHTFOOT obviously embraces several species now 

 considered distinct. 



5. O. macularis, crust roughish, brownish-black ; apothecia clus- 

 tered, roundish-elliptical, rugose, irregular, black. HOOK. Scot. 

 ii. 43. O. epiphega, Eng. Bot. t. 2282. Graphis macularis, SPRENG. 

 Syst. Veg. iv. 250. Lichen rugosus, L.IGHTF. Scot. 802. WITH. 

 iv. 4. 



Ha b. On the smooth bark of trees, of young oaks in parti- 

 cular, common. 



Forms black roughish spots or patches. The branches of 

 young oaks are sometimes so completely overrun with it, 



