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



or sometimes spreadiDg 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, more 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. Ardellcs 

 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. cinnabarinunij T. & B. Ardellae somewhat convex, powdery, 

 vermilion-coloured. 



" Thallus thin, nearly white, smooth, or but slightly 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. 



/5. 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 ot." Lich. Brit. /. c. 



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



y. 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 very edges alone 

 being powdery and red. 



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



