Rev. W. A. Leighton on the British Graphidese. 389 



"Arthonia marginata, Dufour, Jouni. Phys. 8/. 205." (1818) (fide Fries 



et Sehajrer). 

 Platyqramme Lyellii, Meyer in Spreng. Syst. Veg. 4. p. 1. 255 (excL E. Bot. 



1813) (1827). 



New Forest, Hampshire ! Mr. Lyell in herb. Borrer. 



Thallus thin, membranous, of a dull dirty yellow or olive colour, 

 smooth and waxy in appearance, very similar to some states of 

 Verrucaria nitida, Schrad., limited by a dark brown wavy irre- 

 gular line. Lirellce numerous, scattered irregularly, more or 

 less crowded, prominent and sessile, oblong or linear- oblong, 

 rounded and obtuse at each extremity, for the most part simple, 

 straightish, the margin variously waved and curved, occasionally 

 branched, though apparently in general the result of confluence ; 

 — there are also smaller lirellse of an irregular rounded form in- 

 terspersed. Disk broad, flat or concave, of a dull dark brown, 

 more or less pruinose, surrounded by a narrow prominent ele- 

 vated wavy black proper margin, and encompassed by an elevated 

 rounded spurious thallodal margin, very conspicuous by its white 

 colour and pulverulent appearance. A vertical section shows 

 the perithecium to subtend the base of the disk, just as in an 

 Opegrapha, not at all resembling the lig. 2 of the genus Leior- 

 reuma in Eschweiler's Syst. Lich. 13, though the author remarks, 

 " anatomiam optime reprsesentat 111. Sowerbyus icone Opegraphce 

 Lyellii ejus (Eng. Bot. vol. 27. tab. 1876),^^ where the structure 

 is identical with our Plate VII. fig. 24 a. 



The structure of the lirella distinguishes it from Gi-aphis 

 Smithii [Opeg. scripta, E. Bot.), and that together with the 

 sessile lirellse with their white thallodal margin and its general 

 habit from Hymenodecton dendriticum. 



Plate VII. fig. 24. a. Vertical section of thallus and lirella; b. sporidia. 



5. Aulacographa. 



Apothecium lirellseform, subimmersed, prominent; perithe- 

 cium carbonaceous, dimidiate or confined to the sides, palmatifid, 

 the base naked ; disk rimseform, closed, surrounded with a proper 

 longitudinally furrowed margin and an accessory thallodal margin. 

 Thallus membranaceous. 



Name from avXa^, a furrow, and ypacj)?}, writing, in allusion 

 to the furrowed proper margins. 



1. Aulacographa elegans. Thallus membranaceous, subtarta- 

 reous, orbicular, granulated or rugose, determinate; lirellse 

 erumpent, prominent, sessile, oblong or lineari-elongate, simple, 

 straight or curved ; proper margin thick, tumid, prominent, lon- 

 gitudinally furrowed ; thallodal margin thin, membranous ; disk 

 rimseform ; sporidia in asci, lineari-elongate, with a broad mem- 



