Lecanora helicopis

A strictly coastal species that is found on sheltered siliceous rocks in the supralittoral zone. The thallus is grey and rimose with a defined prothallus. The small apothecia have blackish discs and pycnidia are typically numerous. Often grows with Myriolecis actophila, with which it can be confused. 

Listed by Alan Orange in Flora of Glamorgan (Wade et al, 1994).