Rev. W. A. Leighton on the British Graphidese. 267 



shining or dull, generally with more minute granulations or 

 rugosities especially about the lirellse, whence and from their 

 more crowded condition the plant assumes a pulverulent or ashy 

 and dusty appearance ; in some instances becoming ashy- 

 coloured and densely rugose from the thickly crowded lirellse. 

 Lirellcs very numerous and crowded, variable in form and size, 

 straightish or curved, some of them long, simple, straightish and 

 wavy, others simply curved, others curved back on themselves, 

 others short and variable in curvature, either with a single 

 branch from the centre at right angles, or two or three in a sub- 

 stellate form ; others simple at one extremity, with one, two, or 

 three branches at the other ; others again furcate, or simply and 

 shortly branched at both extremities ; others bent into a right 

 angle. The general character and habit resemble all the pre- 

 ceding. 



The form and habit of the lirella form the chief distinctive 

 characteristics between Graphis scripta and G. pulverulenta and 

 their respective varieties or forms. In G. scripta it is emergent j 

 as Acharius expressly says, the uplifted and rifted thallus form- 

 ing a thin membranous thallodal spurious margin to the lirella, 

 whose proper margins are thin and elevated, encompassing the 

 naked rimseform disk in a wavy, flexuose, irregular manner, nar- 

 row and nearly parallel at the one extremity, with a linear-lan- 

 ceolate elongato-acuminate expansion at the other. 



In G. pulverulenta the lirella seems uplifted and sessile on or 

 amid the thickened swollen thallodal margins, the proper mar- 

 gins thick and uniform, encompassing in a bold uninterrupted 

 and nearly parallel curving the uniformly expanded pulverulent 

 disk ; the extremities being acute, often with a peculiar curve 

 giving to a branched lirella somewhat of a hastate shape. 



From Graphis serpentina both are separated by the sporidia. 

 I at one time fancied that the sporidia in G. scripta were of a 

 regular elliptical shape, those in pulverulenta being oblong, but 

 I think not so constantly so as to be distinctive, intermediate 

 variations in form having been noticed in both. However the 

 hint is thrown out for further observation. 



The sporidia prove all the specimens of Opegrapha scripta in 

 Schserer's * Lich. Exsicc.^ to be in reality forms of Graphis ser- 

 pentina. 



G. scripta, pulverulenta, and serpentina have been so confounded 

 togethtT by authors generally, that without the examination of 

 -authentic specimens of the varieties of eacli, it seems to be a 

 mere hopeless guesswork to attempt an arrangement of the 

 synonyms. Nothing but the sporidia can distribute them cor- 

 rectly. 



