338 SYSTEMATIC 



Lecanora, Ochrotechia^ Lecania, Haematomma and Phlyctis are cosmo- 

 politan genera, some of them with a very large number of species ; the other 

 genera are more restricted in distribution and generally with few species. 



The genus Candelariella is of uncertain position; the spores are 8 or 

 many in the ascus and are simple or I -septate, and not unfrequently become 

 polarilocular as in Caloplacaceae, but there is no parietin present. 



Algae distributed through the thallus. Spores simple i. *Harpidium Koerb. 

 Algae restricted to a definite zone. 

 Spores simple. 



Thallus grey, white or yellowish. 



Spores rather small 2. Lecanora Ach. ., 



Spores large 3. Ochrolechia Massal. 



Thallus bright yellow. 



Spores simple or i -septate 4. Candelariella Miill.-Arg. 



Spores i -septate (rarely pluri-septate). 

 Paraphyses free. 



Thallus squamulose, effigurate 5. Placolecania Zahlbr. 



Thallus crustaceous. 



Apothecial disc brownish 6. Lecania Zahlbr. 



Apothecial disc flesh-coloured 7. Icmadophila Trevis. 



Paraphyses branched, intricate 8._*Calenia Miill.-Arg. 



Spores elongate, pluri-septate. 



Apothecia superficial 9. Haematomma Massal. 



Apothecia immersed. 



Paraphyses free 10, *Phlyctella Miill.-Arg. 



Paraphyses branched, intricate II. *Phlyctidia Miill-Arg. 



Spores muriform. 



Apothecia superficial 12. *Myxodictyon Massal. 



Apothecia immersed 13. Phlyctis Wallr, 



XLVI. PARMELIACEAE 



A very familiar family of foliose lichens. Genera and species are dorsi- 

 ventral and stratose in structure, though some Cetrariae are fruticose in 

 habit. Algal cells are Protococcaceae ; in Physcidia they are Palmellae. In 

 every case the upper surface of the thallus is corticate and generally of 

 plectenchyma, the lower being somewhat similar, but in Heterodea and 

 Physcidia, monotypic Australasian genera, the upper cortex is of branching 

 hyphae parallel with the surface, the lower surface being non-corticate. 



The Parnieliae are mostly provided with abundant rhizinae; in Cetrariae 

 and Nephromopsis these are very sparingly present, while in Anzia (including 

 Pannoparmelia) the medulla passes into a wide net-like structure of anasto- 

 mosing hyphae. 



In Heterodea, cyphellae occur on the under surface as in Stictaceae; arid 

 in Cetraria islandica bare patches have been described as pseudocyphellae. 

 The latter lichen is one of the few that are of value as human food. Special 

 aeration structures are present on the upper cortex of Parmelia aspidota. 



