GENERA AND SPECIES. 183 



where it attains considerable thickness, otherwise 

 the apothecia are as in Collema. The spores liave 

 tlie general characters of the spores in Collema. 



There can be little doubt that this genus is simply a 

 somewhat higher evolution than Collema. The two 

 genera correspond in habitat and range. 



Although a considerable number of species are 

 known, we shall content ourselves with the description 

 of a single species. 



1. Leptogium chloromelum. Thallus medium to 

 large, much wrinkled and folded, margin of lobes 

 turned upward, bearing numerous isidioid outgrowths, 

 dark-green. Apothecia medium, margin somewhat 

 elevated, slightly rugose. Disk dark-brown. SjDores 

 colorless, multilocular, granular, 20/a X 12/x. 



3. Hydroihyria. 



Thallus quite large, flat, lobed, dark ; distinctly 

 veined below. The veins are simply bundles of 

 hyphasi. The genus is represented by one species 

 only. It is peculiar in that its habitat is on rock in 

 clear running water, in which position it matures its 

 spores. As a rule, lichens do not thrive in very moist 

 places. Some doubt exists as to the nature of the 

 symbiotic algic. Some authors maintain that they are 

 Rlvularia. They certainly are not normal Rivularia ; 

 it is likely that they are modilied Nostoc. Further 

 study is necessary to determine tliis ])oinr. 



1. Hydrothyria venosa. Tliallus large, tliin, lobes 

 large, smootlu dull gray when dry ; somewhat paler 

 beneath and bearing branching veins. Apothecia few, 



