Confidence: I'm as sure as I can be.
Notes: Hi Jenny, it all depends on which authority one follows. I feel the Dutch research works well in Britain, which, with those abraded margins to the basal squamules makes this good pocillum. The basal squamules are large and imbricated, which also points to pocillum. It would be nice to see apothecia characters but this is certainly not what I regard as "good" pyxidata. However, it may be that we are trying to force more than two taxa into two names, or alternately that we should recognise just the one, variable species. Recent DNA work in Canada suggests there is a complex, with more than one 'pyxidata', one ancestral to the rest of these species.
So to me, your photograph is C. pocillum and convincingly so. I had already noticed it on your site and was planning o take it up with you sometime. I do, incidentally, worry about the 'pocillum' on your site, which I am down as identifying, which indeed I did, though with doubt as I recall. I still think it is probably C. pocillum, but I would not like to be definite. Alan