18 THE T)Eteeminatio:n' of lichens in the field 



2. Ap. immersed and aggregated in wart-like 



portions of the th. (Z>). Sp. septate 13. 



Ap. not aggregated in specialized portions of 



the th. (c), which is usu. thin 3. 



3. Ap. with a proper margin, except in abnormal 



cases or in old plants 5. 



Ap. without proper margin 4. 



4. Ap. usu. roundish, little divided, and with a 



spurious thalline margin. Sp. 3-septate... Platygrapha. 

 Ap. usu. diiform, often divided and without a 



spurious thalline margin. Sp. 1-6-septate. Arthonia (d). 

 Ap. usu. diiform and little divided. Sp. 



muriform Arthothelium. 



5. Ap. irregularly roundish with dark hypo- 



thecium. Sp. 1-5-septate, colourless Lecanactis. 



Ap. typically ± linear, often much elon- 

 gated (f/) G. 



6. Th. with green algal cells. Ap. oblong to 



oval. Sp. simple or 1 -septate 7. 



Th. with orange algal cells. Ap. usu. elon- 

 gate. Sp. 1-many- septate 10. 



7. Sp. 1 -septate, dark brown (colourless when 



young), 15-23 X 8-12 ft. On calcareous 



rocks Eiicephalographa. 



Sp. simple, colourless 8. 



8. Ap. elongate with 2-4 parallel hymenia. On 



wood Ptychographa. 



Ap. with simple hymenium. On rocks or 



wood 9. 



9. Ap. black with narrow disc and prominent 



margin. Hypothecium dark. Usu. on 



rock (e) Lithographa. 



Ap. dark brown or reddish with a dilated 

 disc and less prominent margin. Hypo- 

 thecium colourless or brownish. On trees 

 and palings Xylographa (/ ). 



10. Sp. 1-septate, colourless or brown. On 



trees (y) Melaspilea. 



Sp. 3-many-septate, colourless or brown. On 



trees, rocks, etc 11 . 



Sp. muriform, colourless. On trees Graphina. 



11. Ap. superficial. Paraphyses with transverse 



connections. Sp. colourless, 3-man3^-se2)- 



tate (^) Opegrapha. 



Ap. immersed. Paraphj'ses vertically paral- 

 lel without transverse connections. Sp, 

 colourless or brown, S-man^r-septate 12. 



12. Sp. colourless (h), 7-many-se23tate. Disc of 



ap. usu. narrow Graphis. 



Sp. brown (h), 5-8-septate. Disc, of ap. 

 usu. 4:dilated. Para2)li3'ses usu. less dis- 

 tinctly shown Phaeographis. 



