KEYS TO THE STUDY OF LICHENS. 79 



Tliallus distinctly blue-green to dark-blue, 

 thin, higlily gelatinous when moist. 



Lower surface devoid of long rhizoids, | CoUema. 

 Lower surface bearing long rhizoids, 



thallus comparatively thick .... Mallotium. 



Lower surface veined Hydrothyria. 



Apothecia innate, not cup-shaped. 



On lower surface of upturned lobes . . . Nephromium. 

 On upper surface of thallus. 

 Thallus comparatively small, apothecia 



not marginal Solorina. 



Thallus large, apothecia marginal .... Peltigera. 



Thallus Fruticose. 



Thallus very minute, dark-blue, scarcely visible to the 

 naked eye. 

 Apothecia terminal, more or less globose. 



Thallus-lobes distinctly flattened .... Omphalaria. 

 Thallus-lobcs not distinctly flattened .... Lichina. 



Apothecia lateral, discoid Poiychidium. 



Apothecia within thallus Ephebe. 



Thallus distinct to very large. 



Yellowish coloration in thallus or apothecia. 



Thallus distinctly flattened Theloschistes. 



Thallus not distinctly flattened Evernia. 



Yellowish coloration wanting. 



Thallus flattened, thick, not brown or dark. 



Disk black, thallus gray to purplish . . . Rocella. 



Disk not black, thallus greenish Ramalina. 



Thallus flattened, thin, brown to dark . . . Cetraria. 

 Thallus cylindrical, hollow. 

 Apothecia terminal. 



Disk black PiJophoron. 



Disk brown or red Chdonia. 



Thallus cylindrical, solid. 

 Branches long, pendulous. 



Color green to grayish-green Usnea. 



C Bryopoqon. 

 Color dark to black < Alector'ia. 



Branches rigid, erect. 



Smooth, shiny Sphcerophoi-us. 



Not smooth, warty Stereocaulon. 



