106 LICHENES. [Opegrapha. 



3. O. vulgata, ACH. Thallus leprous, somewhat coarsely 

 powdery, with minute scales, greenish-white ; apothecia sessile, 

 the longer somewhat terete, subrugose, smooth, with a narrow 

 disk. Ach. Lick. Un. p. 255. Eng. Bot. t. 1811. 



On stems of old trees ; near Belfast, Mr. Templeton : on the stems 

 of furze, near Dunkerron, County of Kerry. The variety on furze 

 has the thallus thin, investing, smooth, and shining, nearly white. Mr. 

 Templeton found it with the lirellce, scarcely longer than they are 

 broad, with the thallus powdery, and of a buff colour, inclining to 

 green. 



4. O. varia, PERS. Thallus thin, leprous, powdery, greyish- 

 white ; apothecia sessile, prominent, various in length, the disk 

 wide, flat, at length convex, the margins at length disappearing. 

 f*ers. in Ust. fasc. 7, p. 30, according to Hooker, Eng. Flor. v. 

 5, p. 145. Eng. Bot. t. 1890 and t. 22SO. O. notha, Ach. L. 

 Un. p. 252. 



On the bark of aged trees ; not uncommon. The shape of the 

 disk of the apothecia seems at first to distinguish this from the pre- 

 ceding, but unfortunately in the former it is occasionally very wide, 

 and in the present as narrow as, perhaps, in any other Opegrapha. 



5. O. saxatilis, DE CAND. Thallus tartareous, thin, pow- 

 dery, white, sometimes evanescent ; apothecia sessile, promi- 

 nent, often in small clusters, varying in length, the margins 

 flexuose. De Cand. Fl. Franc, v. 2, p. 312. Eng. Bot. t. 

 1790. 



On rocks, on walls, and on mortar ; not uncommon. On limestone 

 the thallus has sometimes a reddish hue, and the lirellcs are extremely 

 narrow. On siliceous slate in maritime situations there is no vestige 

 of a thallus, but a whitish discolouration of the surface of the rock ; 

 the lirellce are jet black, shining, and clustered. Again, on mortar, as 

 at Kilbarrick Church, near Dublin, the thallus is tartareous, thick, 

 slightly cracked, snow white, somewhat powdery on the surface, and 

 the lirellcs as densely clustered as in O. atra. Future observations 

 may confirm the conjecture that the present is but a rock variety of the 

 preceding. 



6. O. scripta, ACH. Thallus membranaceous, thin, smooth, 

 greyish or greenish white ; apothecia immersed, flexuose, their 

 disk very narrow, having a spurious thallodal border. Ach. 

 Method. Lich. p. 30. Graphis scripta, Ach. Lich. Un. p. 265. 

 Eng. Bot. t. 1754 and t. 2301. 



On the bark of old trees ; not uncommon. The thallus is usually 

 smooth, yet sometimes much wrinkled, thick and powdery on the sur- 

 face. The apothecia vary in length, and have their disk sometimes 

 pruinose : the thallodal whitish border to the lirellce distinguishes this 

 from all the preceding, and the distinct black margins to the disk in a 

 great measure from the following. . 



7. O. dendritica, ACH. Thallus subtartareous, determinate, 

 somewhat powdery, white ; apothecia immersed, flexuose, 

 branched ; the disk flat, with a border from the thallus only. 



