182 



tance. Some authors consider this group very closely related to 

 Urceolaria ; the apothecial characters are, however, essentially 

 different. 



The thallus is mostly epiphloeodal, particularly the older portion, 

 crustaceous, thin, somewhat areolate ; the algae (Cystococcus humi- 

 cola) very rarely occur below the surface of the substratum ; the 

 thallus is attached to the substratum by comparatively long sparingly 

 branched hyphae, which are easily torn loose by heavy winds and 

 rains ; thus it happens that a considerable portion of the thallus is 

 removed, bringing into greater prominence the more firmly attached 

 globose apothecia. 



The apothecia are comparatively large, with a dark perithecium 

 (hypothecium and proper exciple). The pore is quite large and be- 

 gins to form early in the development of the apothecium. The apo- 

 thecium is partly hypophloeodal ; very early in its development it 

 breaks through the thin layer of superimposed cork-tissue. 



The paraphyses are comparatively long, slender, and sparingly 

 branched near the apex ; they also show a decided tendency to be- 

 come granular. The spore-sacs are quite large, cylindrical, each 

 containing eight long colorless spores. It is impossible to confuse 

 these spores with any others ; their extreme length, cylindrical form 

 and numerous transverse septa are striking. 



Only one species has so far been reported, which seems to occur 

 throughout the territory upon trees with comparatively smooth bark, 

 such as Bctula and Acer. 



PLATE 53. 



COXOTREMA URCEOLATUM Tuck. 



1. Natural size, a, apothecia. 



2. Apothecium and fragment of thallus magnified. 



3. Section of apothecium. 



4. Section of thallus. 



5. Paraphyses and spore-sac. 



6. Spores, a, exosporium ; b, cell-lumina. 



4. THELOTREMA Ach. Lich. Univ. 62. 1810. 



This is another group whose position in the system is not defi- 

 nitely determined. Many of the characters met with in Conotrema 

 also present themselves here. 



As in the former genus the thallus is quite rudimentary and partly 



