Rev. W. A. Leighton on the British Graphidese. 91 



Thallus thin, crustaceous, very minutely cracked and crumbly, 

 white or pale yellow, sometimes entirely obliterated. Lirella 

 numerous, crowded together in patches of greater or less extent, 

 sometimes so thickly so as to be heaped together in black plicate 

 or cerebrinal masses. In a perfect state, elongated, linear, of 

 about the same width throughout their whole length, in various 

 ways bent back upon themselves, curved, flexuose and wavy in a 

 very peculiar and remarkable manner, generally quite simple, 

 seldom if ever branched, sometimes subimmersed, at others sessile 

 and prominent, obtuse at the extremities, smooth and somewhat 

 shining or greasy-looking, the margins tumid, round, and in- 

 curved. The younger lirellse are much shorter and not so curved. 

 The disk is a narrow slit of about the same width throughout, 

 which widens in age, and in extreme maturity becomes open and 

 on a level with the margins which are obliterated, but never 

 baggy as in saxatilis. 



Dr. Taylor's specimen was on a slaty rock, entirely denuded 

 of the thallus, with only a whitish discoloration, the lirellse 

 remarkably twisted together in innumerable crowded plicee or 

 gyrations, forming highly prominent, rounded, black shining 

 masses or clusters. I have gathered similar specimens at the 

 South Stacks, Holyhead, and received such from Rev. T. Salwey 

 from Barmouth. Possibly it may be the var. h. steriza, Ach. 

 Syn. 72. 



The strongly curved, elongated, linear, simple lirellse with 

 their singular undulate, wavy and flexuose appearance distin- 

 guish this plant from O. rupestris ; the lirellse and sporidia from 

 O. saxatilis. 



Plate V. fig. 4. a, Vertical section of thallus and lirella; b, sporidia; 

 c, upper surface of thallus and lirellae. 



5. O. rupestris, Pers. Lirellae oblong or oVate, deformed; 

 short, obtuse, variously 1] r.'^.ched, wider at one extremity; spo- 

 ridia eight in asci, clavate, rounded at each extremity, triseptate, 

 pale yellow. 



Lichen Persoonii, Ach. Prod. 19 (1798). 



Opegrapha rupestris, Pers. Ust. Ann. Bot. 11. 20; Fries, L. Ref. 364. 



Persoonii, Ach. Meth. 17 (1803); Sm. E. Bot. 2345; Chev. Hist, des 



Graph. 53. t. 11. f. 2. 



Persoonii », Aoh. L. Univ. 246 (1810); Syn. 71. 



saxatilis, Schii^r. Spicil. 49. 328 (1823-1836). 



saxatilis a, Schscr. Enum. 159 ; Exsic. 94 ! Hook. Br. Fl. 2. 145 (in 



part) (1833). 



Ireland! Miss Hutchins. Netley Abbey! Mr, Lyell; both 

 in herb, Borrer. Barmouth, Merionethshire ! Rev. T. Salwey, 

 Larne, Co. Antrim ! Mr. W. Thompson. Newton Wood, Cleve- 

 land, Yorkshire ! Mr. J. G, Baker, Great Orme^s Head, Caer- 

 narvonshire ! 



