167 



medullary layer is much reduced. This is no doubt for the purpose 

 •of supplying the necessary mechanical support to the slender 

 branches. The algae (Cystococcus humicola) are quite numerous and 

 rather small. The air enters the thallus at the sides, where the cor- 

 tical tissue is very thin and is traversed by breathing canals. 



The apothecia are of medium size, sessile upon the upper surface 

 of the thallus near the middle, hence the older portions ; the 

 thalloid exciple scarcely reaches above the flattened disk ; the 

 epithecium is light brown and the hypothecium colorless, very 

 thick, cortical in structure, and is divided into two layers ; in the 

 upper the cells are elongated at right angles to the surface of the 

 disk ; in the lower, which is by far the thicker, the cells are elongated 

 vertically to this surface. 



The paraphyses are simple and colorless. The spores are rather 

 small, elliptical, colorless and distinctly two-celled ; the two cells 

 are not, however, united by a plasmic thread, which excludes the 

 genus from the Physciaceae. 



S. euploca seems to be southern and western in its distribution, 

 and is certainly very rare in the eastern United States. It occurs 

 upon rocks. The specimens which came to my notice were associated 

 with a species of Collema. 



PLATE 43. 



Speerschneidera euploca (Tuck.) Trev. 



1. Thallus natural size, a, apothecia. 



2. Portion of thallus magnified. 



3. Section of apothecium. 



4. Section of thallus. 



5. Paraphysis and spore-sac. 



6. Spores. 



7. Algae. 



6. Parmelia Ach. Lich. Univ. 89. 1810. 

 It is highly probable that this group is phylogenetically derived 

 from Lecanora, as there is certainly a close similarity between the 

 higher Lecanoras and lower Parmelias. 



The thallus in this genus is foliose and shows a distinct dorsi- 

 ventral structure. There is no indication of any fruticose tendency. 

 In the majority of representatives dichotomous branching of the 

 J 3 



