134 GUIDE TO THE STUDY OF LICHENS. 



the disk. In the immersed apothecia the disk is ir- 

 regular in outline. The spores are dark in the major- 

 ity of species. The algae are Protococcus (excepting 

 R. oreina). 



The Rinodinas are quite common throughout the 

 United States, but have a slight western and southern 

 tendency. They occur uj^on rock and bark, less com- 

 monly upon soil and moss. 



1. Rinodina constans. Thallus thin, evenly spread- 

 ing, granular to areolate, grayish-green. Apothecia 

 small to medium. Thalloid exciple slightly raised 

 above the dark disk. Spores brown, 17/x, X 8.5/x.^ 



2. Rinodina Bishoffii. Thallus varies from thinly 

 granular to quite thick and indistinctly areolate, brittle, 

 closely adnate though readily removed, often leaving 

 the apothecia behind. Apothecia rather small, slightly 

 raised above the thallus. Disk flattened, black. Spores 

 dark-brown, connecting thread often indistinct, sep- 

 tum thick, 17/x X 12/A. 



3. Rinodina sophodes. Thallus of rather indistinct, 

 more or less scattered, irregular areoles, grayish-green 

 above, dark beneath. Apothecia small. Thalloid 

 exciple, usually deficient. Disk black. Spores brown, 

 slightly constricted at the middle, 22/x X 8/x. 



J/.. Rinodina oreina, Thallus distinctly areolate, 

 comparatively thick, lemon or sulphur color. Apothe- 

 cia immersed, small to medium. Disk black or dark- 

 brown. Spores dark-brown, connecting thread not vis- 

 ible, septum thick, somewhat constricted, 10/x X 6.5/a. 



1 Other generic spore-charactera .are given in the family descrip- 

 tion, which see. 



