If it's brown and pored on the underside then a Coltricia - but if there are teeth/spines on the underside then a species of Phellodon (or a related genus).
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.