i6i 



Celraria, usually occurring near the margin or younger portion of 

 the thallus ; they frequently occur near the base of apothecia, but I 

 have not found such occurrence to be constant. Sometimes the sper- 

 magonia are wholly or almost wholly wanting. 



Key to the Genera. 

 Thallus crustaceous, areolate, to thickly warty, and minutely foliose. 

 Spores multiiocular, dark. i. Urceolaria. 



Spores 4-6-septate, acicular, colorless. 2. Haeniatomma. 



Spores simple, colorless. 3. Lecanora. 



Spores very minute, numerous. 4. Acarospora. 



Thallus foliose, lobed or branching. 



Spores two-celled, colorless. 5. Speerschneidera* 



Spore simple, colorless. 6. Parmelia. 



Thallus fruticose. 



Lobes of thallus distinctly flattened. 

 Spores simple, colorless. 



Thallus-lobes much flattened ; structure centric. 



7. Cetraria. 

 Thallus-lobes less flattened ; structure radial. 



8. Evernia. 

 Spores two-celled, colorless. 9. Ramalina. 



Lobes of thallus cylindrical, filamentous, radial in structure. 

 Central hyphal bundle wanting. 



Spore-sacs with 2-4 spores ; exosporium thick. 



10. Alectoria. 

 Spore-sacs with 8 spores ; exosporium normal. 



1 1 . Bryopogon. 

 Central hyphal bundle present. 12. Usnea. 



i. Urceolaria Ach. Lich. Univ. 74. 1810. 



There is some hesitation about placing this group with the Parme- 

 liaceae because of the immersed apothecia. At first it may seem that 

 the prevailing characters point toward the Verrucariaceae,but on closer 

 examination it is, however, found that the apothecia are not globose 

 and that the paraphyses are not gelatinous. 



The thallus is crustaceous, usually quite thick, areolate, the areoles 

 becoming distinctly convex, or warty in some species ; there is a 

 semicortical upper layer, followed by the algal layer ; the medullary 

 layer is well developed and forms the greater thickness of the thallus ; 

 there is no evidence of lower cortical tissue. The rhizoidal hyphae 



