GENERA AND SPECIES. 145 



absence of blue-green algje ( CyanophycecB) finally 

 separates it from the Collemacece and Pannariacece. 



KEY TO THE GENERA. 



Thallus crustose and areolate to thickly 

 warty and minutely foliosc. 

 Spores not simple. 



Multilocular, dark 1. Urceolaria. 



Five to seven-celled, acicular, color- 

 less 2, Hiematomma. 



Spores simple, colorless. 



Usual size and number (8) .... 5. Lecanora. 

 Very minute and numerous (200) . 4- Acarospora. 

 Thallus foliose, lobed or branching, spores colorless. 



Spores two-celled <5. Speerschneidera. 



Spores simple. 



Thallus greenish, lobes never erect . 6. Pannelia. 

 Thallus brownish, lobes sometimes 



erect 7. Cetraria. 



Thallus fruticose. 



Lobes distinctly flattened, spores colorless. 



Spores two-celled 8. Ramalina. 



Spores simple 9. Rocella. 



Lobes not distinctly flattened, yellow- 

 ish 10. Evernia. 



Lobes cylindrical, filamentous and 

 very long, spores simple. 

 Central hyp ha I core wanting. 



Thick exosporium 11- Alectoria. 



Normal exosporium 12. Bryopogon. 



Central hyphal cores present . . .13. Usnea. 



1. Urceolaria. 



Thallus crustose, usually quite thick and areolate, 

 the areoles becoming distinctly convex or warty in 

 some species. Tlie prevailing color of the upper sur- 

 face is gray, lower surface whitish. The algaj are 

 no doubt Protococcus ; they usually occur in groups 

 of six to twelve, tlius differing from the usual forms 

 which occur singly. 



