BRITISB: LICHENS : 



37. TJsnea Dill. Thallus filamentose, internally with chondroid 

 axis: apothecia terminal or lateral, the margin often ramuloso- 

 ciliate, concolorous, with simple spores ; spermogones with simplish 

 sterigmata and straight spermatia. 



Tribe XI. ALECTORIEI Nyl. Thallus much branched, rounded 

 or compressed, with woolly medulla : apothecia parmelioid, scutelli- 

 form. 



38. Alectoria Ach. Thallus usually filamentose and intricately 

 branched ; medulla arachnoid or lacunose : apothecia terminal or 

 pseudo-terminal, discolorous, with simple or very rarely murali- 

 divided spores ; spermogones with pauci-articulate sterigmata and 

 acicular straight spermatia. 



Tribe XII. CETRARIEI Nyl. Thallus fruticulose or foliaceous, 

 with white woolly medulla : apothecia parmelioid, marginal, obliquely 

 affixed. 



39. Cetraria Ach. Thallus fruticulose, laciniose, rarely fistulose : 

 apothecia subconcolorous, with simple spores ; spermogones with 

 simple sterigmata and cylindrical spermatia. 



40. Platysma Nyl. Thallus fruticulose or membranaceo-lobed : 

 apothecia discolorous, with simple spores ; spermogones with simplish 

 or pauci-articulate sterigmata, and various (not cylindrical) sper- 

 matia. 



Series IV. PHYLLODEI Nyl. ThaUus foliaceous, usually 

 depressed, lobate: apothecia generally parmelioid or lecanorine, 

 discolorous. 



Tribe XIII. PARMELIEI Nyl. ThaUus frondosely dilated, or 

 lobate, or laciniate, with woolly, rarely solid medulla: apothecia 

 panneleine rarely lecanorine. 



41.' Evemia Ach. Thallus laciniose or much branched, flaccid ; 

 medulla arachnoid or partly chondroid : apothecia lateral with simple 

 spores; spermogones with pauci-articulate sterigmata and acicular 

 straight spermatia. 



42. Parmelia Ach. ThaUus variously lobed or laciniate, usuaUy 

 fibrilloso-rhizinose, rarely glabrous beneath ; medulla woolly, lax : 

 apothecia superficial, with simple spores ; spermogones with pauci- 

 articulate sterigmata and acicular apicaUy fusiformi-incrassate 

 spermatia. 



43. Parmeliopsis Nyl. ThaUus steUato-laciniate, sparingly rhizi- 

 noso beneath ; meduUa woolly, lax : apothecia superficial, with simple 

 spores ; spermogones with simple sterigmata and cylindrical arcuate 

 spermatia. 



