120 GUIDE TO THE STUDY OF LICHENS. 



the umbilicus. The margin is generally somewhat 

 torn. The prevailing color of the upper surface is 

 gray to nearly black ; the lower surface is quite 

 black, bearing black rhizoids or scaly lamina. 



The apothecia are rather peculiar in structure. 

 They are sessile upon the thallus, and on examina- 

 tion with a pocket-lens the disk presents a convo- 

 luted appearance, reminding one of the convolutions 

 of the dentine in the tooth of a ruminant. The disk 

 is convex, black. The spores are simple, elliptical, 

 colorless. 



The Gyrophoras are northern in their range, but 

 are also quite common in the mountainous regions of 

 the temperate and torrid zones. They grow upon 

 rock and soil. Quite generally this group is com- 

 bined with Umhilicaria. 



1. Gyrophora hyperhorea. Thallus medium, nearly 

 entire, margin somewhat incised and torn, rugose 

 above, dark to black; usually smooth and some- 

 what lighter below. Apothecia small to medium. Disk 

 flattened, black. Spores ovoid, colorless, somewhat 

 curved, 14/x by 7/u,. 



2. Gyrophora prohoscidea. Thallus medium size, 

 somewhat lobed or folded, and rugose above, margin 

 torn and occasionally perforate, bearing cilia, gray, 

 dark near margin ; lower surface pale toward centre, 

 becoming darker toward margin. Apothecia of me- 

 dium size, scattered over the thallus, except at the 

 centre and margin. Disk flattened, black. Spores 

 simple, colorless, elliptical or ovoid, slightly curved, 

 16ft X 7ft. 



