4*44' Rev. W. A. Leighton on the British Graphidese. 



or sometimes spreading more widely '^ (limited by an irregular 

 wavy watery brown margin), '^in general so very thin as to look 

 little more than a stain on the bark, r^ore rarely a little tar- 

 tareous, continuous or slightly cracked, externally gray, white, 

 or with a pale bluish tinge, green within, its surface generally 

 smooth and polished, but sometimes a little powdery. Ardell<B 

 very numerous, most variable in shape and size, but usually 

 roundish, more or less convex, and scarcely so large, taken 

 singly, as poppy-seed, generally however aggregate and con- 

 fluent in clusters, which are regularly disposed over the whole 

 thallus : these clusters, again, are of a very uncertain figure, but, 

 like the single ardellse, for the most part roundish, often so dis- 

 posed as to appear more or less lobed or stellate, and sometimes 

 too, though much more rarely, oblong, or linear and flexuose, 

 like the lirellse of many Opegraphce." (Lich. Brit. 43.) Disk 

 flattish, depressed or somewhat convex, covered more or less with 

 a bright cinnabar-red powder. The internal structure is pre- 

 cisely similar to that of the genus Arthonia. Sporidia in asci, 

 eight, of an obovate or clavate form, 4-septate, the upper cell the 

 largest, pale red. 



The following varieties are enumerated by the learned authors 

 of the ' Lichenographia Britannica ' : — 



a. cinnaharinum, T. & B. Ardellse somewhat convex, powdery, 

 vermilion-coloured. 



" Thallus thin, nearly white, smooth, or but shghtly rugose, 

 generally more or less cracked, but not unfrequently tinged with 

 a pale bluish hue and truly continuous.^' Lich. Brit. /. c. 



On the bark of smooth trees : common. Sussex ! Mr. Borrer. 

 On hazel in the dean at Pease-bridge, Berwickshire ! Dr. G. 

 Johnston. 



^. rosaceum, T. & B. ! Ardellse collected in flat clusters, 

 which have the appearance of being lobed, powdery, vermilion- 

 coloured. 



" Thallus smooth, white, very slightly cracked, thicker than 

 in a." Lich. Brit. /. c. 



On an old oak on Poyning's Common, Sussex ! Mr. Borrer. 



ry. marginatum, T. & B. ! Ardellse somewhat convex, parti- 

 coloured, chiefly powdery on the margins. 



The central part of the disk of the ardellse is either naked and 

 blackish, or pruinose with a whitish powder, the vei-y edges alone 

 being powdery and red. 



On the bark of smooth trees : common. Sussex ! Mr. Borrer. 



