THELOTREMA. 



299 



from the surrounding tissues. The sterigmata are slender 

 and straight filaments; the spermatia straight and acumi- 

 nate at the extremities. In addition to the ordinary struc- 

 tural elements, the cavity of the spermogones contains a 

 loose network of long ramose filaments embedded in a trans- 

 parent mucilage. 



Genus V. THELOTEEMA, Ach. 



Gen. Char. Thallus crustaceous-cartilaginous. Apothecia ver- 

 rucseform ; exciple thalline, at first closed ; thalamium deeply 

 sunk, ultimately collapsed, depressed, rigid, enveloped in a dis- 

 crete, membranaceous, lacerate-dehiscent, interior exciple. (Name 

 from 6r}\r), a wart, and rprj^a, a perforation, in allusion to the 

 form of the apothecium.) 



1. Thelotrema lepadinum (\e7ra?, a limpet). Thallus 

 membranaceous-cartilaginous, whitish, effuse. Exterior ex- 

 ciple of apothecium superficial, truncate-conical, with an en- 

 tire margin, — internal one vaulted, with a lacerated margin, 

 enclosing a blackish, at first greyish-pruinose thalamium, 

 apothecia at length becoming urceolate-scutelliform. Spores 

 large, fusiform, pale yellow, cellular. (E. B. 678.) 



On the bark of trees in lowland and subalpine districts ; 

 not very common. Its thecse are large and two or three- 



