Opegrapha.} LICHENES. 105 



cimens ; varies, too, in having 1 the surface nearly entire or cracked into 

 scales. 



4. A. ilicina. Thallus membranaceous, thin, smooth, whitish 

 or cream-coloured, at length breaking into contiguous scales, 

 with a thin, brownish border; apothecia large, angulate, or 

 oblongo-subrotund, flat ; the disk black, often cracked, with a 

 narrow thallodal border when dry. 



On old stems of holly in woods at Killarney ; not rare. The patches 

 are usually considerable in size, sometimes three or four inches in dia- 

 meter, closely investing the bark. The breadth of the border to the 

 thallus varies, but is always distinctly marked in contact with other 

 lichens. The apothecia, by no means crowded, are yet remarkable, 

 from their size, being sometimes nearly a line in diameter ; they are 

 half immersed, when wet they swell, become convex and prominent ; 

 they have no proper margin ; their disk is black ; their lamina prolig era 

 of an olive brown, semitransparent, and showing vertical striae. Per- 

 haps, this may prove to be only a state of A. gyrosa, Ach. this last, 

 however, is smaller in all its parts, the apothecia are more numerous, 

 and more confluent, and their margins appear irregularly incised or, 

 as Acharius defines them, " gyroso-rugosi? of which there is not the 

 least appearance in our plant. 



19. OPEGRAPHA, Ach. 



Thallus crustaceous, membranaceous or leprous, uniform. Apo- 

 thecia oblongo-elongated, immersed or sessile, covered by a 

 dark membrane ; the disk black, narrow, with a proper bor- 

 der. 



1. O. epipasta, ACH. Thallus membranaceous, very thin, 

 somewhat determinate, shining, grey or pale copper-coloured ; 

 apothecia minute, immersed, scattered, slightly convex, short, 

 mostly simple, with a very narrow border. Ach.L. Un.p. 258. 

 Eng. Bot. t. 40, scarcely t. 1828. 



On lime trees, near Belfast, Mr. Tentpleton. 



2. O. atra, PERS. Thallus membranaceous, very thin, smooth, 

 grey, olive-grey, or pale ferruginous ; apothecia subsessile, the 

 smaller punctiform or globose, the larger elongated, narrow, 

 somewhat wrinkled, flexuose, coal-black, simple or divided, 

 Pers. in Ust. Ann. fasc. 7. p. 30, /. 2. C. c. according to Hook, 

 in Eng. Flor. v. 5, p. 145. Eng. Bot. 1. 1 753 ; also t. 1347 and 

 t. 1789. 



On the bark of trees ; common : rarely on rocks, as at Dunkerron 

 Mountain. Specimens occur on ash trees, at Dunkerron, so exactly 

 intermediate that I do not think they can be more strictly referred to 

 O. rufescens, Pers. than to the present species : but the former is by no 

 means rare on oaks and other trees in the South of Ireland ; it is even 

 to be observed on siliceous rocks. This plant varies by the colour of 

 the thallus, its thinness, its continuity, or being occasionally broken 

 into little scales, by the length of the apothecia, by their dispersion, by 

 their confused or stellulate aggregation. 



