GENERA AND SPECIES. 123 



large, entire, margin somewhat lobed or torn ; upper 

 surface smooth, centre raised, gray to brown; lower 

 surface dark. Apothecia medium to large, scattered, 

 convex, black. Spores large, colorless, simple, very 

 granular, ovoid, not curved, 24/x X 12/x. 



16. Umhilicaria. 



The general appearance and structure of the thallus 

 and apothecia of Umhilicaria shows its close relation- 

 ship to Gyrophora. It differs, however, in that rhi- 

 zoids, cilia and scaly plates (lower surface) are want- 

 ing. Coloration is the same in both. In Umhilicaria 

 the thallus is more or less pustular. The important 

 distinguisliing characters occur in the spores, wliich in 

 this genus are large, brown-colored, multilocular, each 

 spore-sac bearing a single spore. 



The algae in Gyrophora and Umhilicaria are evi- 

 dently Protococcus, though they differ in form from 

 those occurring in other lichens ; further investigation 

 may prove it another alga. 



The range and habitat of this group is much as 

 that of the preceding. It is represented by fewer spe- 

 cies. When dry, these lichens are very brittle, hence 

 the collector will find it necessary to gather them 

 when the atmosphere is moist, or to pour water upon 

 them before attempting to remove them from the rock 

 upon whicli they grow. 



1 Umhilicaria papulosa. Thallus medium to 

 large, thin, margin more or less lobate and torn; 

 pustular, pustules quite separate and uniform in size ; 

 dark-gray above; lower surface reticulately pitted. 



