Confidence: I'm as sure as I can be.
Notes: Yes, could be C. vitellina, probably is, but these states with dispersed areoles (i.e. not a continuous thallus) need microscopic checking. I cannot rule out C. aurella. Good example of Porpidia tuberculosa to the right (pale grey thallus with blue-grey soralia on the surface beginning to join up into a single layer of dark soredia).