I bought a lot of Domitian and Vespasian As coins, and this random object was thrown in the mix. Any ideas? My best guesses are: 1. Lid to a small jar/container of some sort. 2. Small ritual offering dish. 3. World's smallest kylix. It certainly looks ancient, and came with similar patination/encrustation as the coins it came with.
A.C.H. is probably right, but there is a possibility it could be a detached lid from a bronze oil lamp .