16 THE DETEinilXATIOX OF LIOilEXS IX THE FIELD 



9. Algal cells. Bivularia. Tli. corticate. Ap. 



without thalline margin. Sp. 1-3-septate. Pterygium. 

 Algal cells Gloeocapsa or Chroococcus. Tli. 

 not or slightly corticate. Ap. with or 

 without thalline margin. Sp. simple 10. 



10. Algal sheath yellow. Th. slightly corticate. 



Ap. usu. innate and zbclosecl. Paraphyses 



unseptate \.... Psorotichia. 



Algal sheath reddish. Th. not corticate ... 11. 



11. Ap. usu. innate (/") and _h closed. Para- 



physes unseptate Pyrenopsis. 



Ap. open or plane. Paraphj^ses septate Euopsis. 



(rt) If the reproductive organs are perithecia, see Table H. Not 

 corticolous except in some species or forms of Leptof/ium, Pannaria, 

 and Farmeliella. 



(b) See note^ on Sectional Key B. 



(c) In some species of Leptogiuni {Collemodium) the cellular 

 nature of the cortex is often indistinct. G-ranular forms of Collema 

 ckeileum may have the fungal filaments and algal cells so closely 

 packed that the structure may be mistaken for a cellular one. 



{d) Collema 1-8 (or forms of these species). 



(e) P. niqrum is a very common lichen on calcareous rocks. 

 When typical it is easily distinguished by its hypothallus extending 

 as a dark-blue band from the margin of the subdeterminate, minutely- 

 coralloid, dark th. 



(y) An ap. is said to be adnate when its base is surrounded by 

 the th., innate when surrounded by the th., and immersed when 

 deeply seated in the th. 



E. THA.LLUS CRUSTACEOUS OR WAXTIXG. APOTHECTA OR PERI- 

 THECIA IMMERSED IX PITS OF THE ROCKY SUBSTRATUM. 



1. Thecia with open discs (apothecia) 2. 



Thecia with disc opening by a minute ])ore 



(perithecia) 4. 



2. Ap. flesh-coloured or dark, with thalline 



margin 3. 



Ap. dark, without thalline margin. Sp. 

 simple, colourless Lecidea immersa and L. metzleri. 



3. Ap. flesh-coloured. Sp. simple, colourless . Aspicilia prevostii. 

 Ap. dark. Sp. 1-septate, brown or dark. 



Rinodina bischoffii v. immersa. 



4. Sp. simple 'J- 



Sp. 1-3-septate or murif orm 0. 



5. Perithecium with fissured apex. 



Verrucaria (Limborina) calciseda. 

 Perithecium without fissured apex Verrucaria («). 



6. Sp. 1-septate • • . 7. 



Sp. 3-septate (occasionally with a longitu- 

 dinal septum Thelidium incavatum. 



Sp. murif orm Polyblastia schraderi and P. deminuta. 



