GENERA AND SPECIES. 177 



these minute lobes usually occur in close proximity. 

 The algje are Pleurococcus as in Verrucaria. 



The apothecia are very small, usually one is im- 

 mersed in each thallus-lobe- Quite generally minute 

 single-celled algse {^Pleurococcus'^) occur above the 

 thecium ; these are known as thecial algse, and are 

 ejected with the spores and enter into a symbiotic re- 

 lationship with the germinating spore. The spores 

 are colorless, multilocular, thus differing from those of 

 Verrucaria and Endocarpon. 



The only species occurs upon limestone, and seems 

 to be southern in its range. 



1. Dermatocarpon pusillum. Thallus-lobes entire, 

 minute, widely scattered, closely adnate to the substra- 

 tum, dark. Apothecia typical of the genus. Spores 

 typical, two or three in each spore-sac, 23.5/x X 18.5/x. 



9. Endocarpon. 



In this genus the thallus is large, typically foliose, 

 entire ; attached by a central portion (umbilicus) con- 

 sisting either of a single lobe or numerous, more or 

 less plicate, lobes. The thallus is quite thick and rigid 

 and much less brittle than in Umbilicaria and Gyro- 

 phora. Color gray to dark-gray. 



The apothecia are small, globose and entirely im- 

 mersed in the thallus, opening by small dark pores, 

 which are scattered over the thallus. The spores are 

 simple, colorless, elliptical, the usual number (8) oc- 

 curring in each spore-sac. 



The Endocarpons occur principally upon rock, also 

 upon soil and the bark of trees. 



