b BKITISH LICHENS : 



37. Usnea Dill. Thallus filamentose, internally with chondroid 

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

 cihate, eoncolorous, 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, seutelli- 

 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 

 acieular straight spermatia. 



Tribe XII. CETRARIEI Nyl. ThaUus fruticulose or foliaceous, 

 with white woollj^ medulla : apothecia parmeHoid, marginal, obhquely 

 affixed. 



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

 apothecia subconcolorous, with simple spores ; spermogones with 

 simple sterigmata and cylindi'ical spermatia. 



40. Platysma Nyl. ThaUus fi-uticulose or membranaceo-lobed : 

 apothecia discolorous, with simple spores ; spermogones with simpUsh 

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

 matia. 



Series IV. PHYLLODEI Nyl. ThaUus foliaceous, usuaUy 

 depressed, lobate : apothecia generaUy parmeUoid or lecanorine, 

 discolorous. 



Tribe XIII. PARMELIEI Nyl. ThaUus frondosely dUated, or 

 lobate, or laciuiate, with woolly, rarelj' solid meduUa : apothecia 

 parmeleiue rarely lecanorine, 



41. Evernia Ach. ThaUus laciniose or much branched, flaccid : 

 meduUa arachnoid or partly chondroid : apothecia lateral with simple 

 spores; spermogones with pauci-articulate sterigmata and acieular 

 straight spermatia. 



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

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

 apothecia superficial, with simple spores ; spermogones with pauci- 

 articulate sterigmata and acieular apieaUy fusiformi-incrassate 

 spermatia. 



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

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

 spores ; spermogones with simple sterigmata and cyUndrical arcuate 

 spermatia. 



