Sorry, couldn't get under this one. I do have a few other similar ones from the area I have yet to upload, so perhaps one of them may have the underside...
Coltricia is a possible genus and that would be confirmed if the underside were pored. Coltricia is a common but there are one or two genera which, from above, can look a little like Coltricia, but with a dense mass of short teeth or spines on the underside of the cap. While I will call this Coltricia, that is based on probability, rather than certainty.