Lecanora muralis (Schreb.) Rabenh.
Pale greenish-grey to yellow-grey crustose thallus with clearly lobed outer margin. Apothecia with brown or creamy-brown discs with crenulate margins. On siliceous, bird-enriched rocks and concrete
Smith, C.W. et al. editors (2009) The Lichens of Great Britain and Irelandd
Dobson, F.S. (2018) Lichens: an Illustrated Guide to the British and Irish Species