254 POPULAR HISTORY OF LICHENS. 



white ; lirelke oblong or linear-oblong, rounded at each end, 

 simple, curved; proper margin stout, elevated, wavy; tha- 

 lamium flat, dilated, pruinose. Spores fusiform, seven- sep- 

 tate, pale yellow. (E. B. 809.) 



On old oaks, and on oak timber long exposed to the 

 weather, in various parts of England. It closely resembles 

 in general appearance the corticolous forms of Lecidea albo- 

 atra, var. corticola, from which however its spores will dis- 

 tinguish it. Some authors regard many of the Graphidece 

 as deformed Lecideas, and assert that in temperate climates 

 Opegrapha frequently reverts to its normal type Lecidea. 



Genus VII. PLATYGBAMMA, LeigU. 



Gen, Char. Apothecium lirellate, subsimple or radiate. Peri- 

 thecium none ; thalamium free, plane, open, naked, without any 

 margin. Thallus crustaceous. (Name from 7r\aTvs, broad, and 

 ypdfjLfxa, a letter.) 



1. Platygramma Hutchinsle. Thallus minutely 

 cracked ; lirellse immersed in elevated thalline verrucae, ob- 

 long or elongated, simple or branched, straight or flexuose ; 

 thalamium plane, dilated, naked. Spores fusiform, five to 

 seven-septate, pale yellow. 



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