Confidence: It's likely to be this, but I can't be certain.
Notes: If recognised at all, generally regarded as a var. of H. conica, and it is probably best to wait on taxonomic, DNA and nomenclatural clarification of this group at present. However, the photo does seem to represent H. tristis very well, and in my own experience it seems to behave like a distinct species. Lacks the bright colour of H. conica and has a subtly different cap shape, or so it seems to me.