Rev. W. A. Leighton on the British Graphideae. 211 



partially cracked where it is thicker in substance amidst the 

 groups of lii-ellse, where and around the very bases of the lirellae 

 it is chiefly to be distinguished ; in other and opener portions 

 being only a pulverulent film, of a very pale yellowish gray. 

 Lirellce numerous, scattered and difl'use, or closely congi-egated 

 in larger or smaller groups, excessively prominent and sessile, of 

 a dull black colour, more or less sprinkled with the powder of 

 the thallus, lying in all directions, straight or variously cuned, 

 chiefly simple, but here and therewith a simple branch, variable 

 in size, oblong or linear, or linear-elongate, of the same width 

 throughout, obtuse at the extremities, very plump in appearance 

 from the rounded inflexed proper margins, which are rugged and 

 broken. Disk of the same width throughout, distinctly and 

 broadly rimsefonu. 



The size, appearance and habit of the denuded lirellae induce 

 me to present this as a new species, though doubtfully, for the 

 sporidia would lead me to regard it as a variety of siderella. The 

 denuded state of the thallus may arise from local circumstances 

 connected with the nature of the matrix, and the otherwise im- 

 mersed lirellse be thus rendered accidentally prominent. Nor is 

 the difference in size of the lu-ellae between this and the pre- 

 ceding greater than prevails in other species, e. gr. O. rupestris 

 and O. varia. 



Plate VI. fig. 15. c, Plant, nat. size; a, vertical section of thallus and 

 lirella; b, sporidium. 



14. Opegrapha lentiginosa, Lyell MS. Thallus thin, tarta- 

 reous, smooth, cream-coloured, limited ; lirellae excessively pro- 

 minent and sessile, very minute, punctiform, oblong or linear, 

 straight, simple ; disk a mere chink ; proper margins tumid and 

 incurved ; sporidia in asci, eight, irregularly obovate, uniseptate, 

 pale brown. 



On beech and holly in New Forest, Hants ! Mr. Lyell in herb. 

 Borrei-. On beech in St. Leonard's Forest, Sussex, sparingly ! 

 Mr. Borrer. 



Thallus thin, tai-tareous, continuous, even and smooth, here 

 and there slightly and delicately cracked, cream-coloured, form- 

 ing irregularly rounded or oblong or more extended patches, one 

 or two inches in size, bounded by a tolerably broad, irregular, 

 wavy, brownish-black margin. Lirella n\raxexovL% and veiy mi- 

 nute, appearing to the naked eye as mere black specks, under a 

 lens like a multitude of minute black gi-ains of wheat scattered 

 over the thallus and lying in all directions, either singly or 

 confluent and crowded, variable in size, the smaller or younger 

 ones punctiform and more or less imbedded in the thallus, the 

 larger and perfect ones of a narrow linear-oblong form, shghtly 



14* 



