At 17mm I think we are seeing a bit too much completeness of the design for a dupondius. Given the radiate obverse, I prefer to think it is an antoninianus. I like Ben's suggestion, or one of the Gallic emperors. As for the "C" in the right field, not sure what to make of it, or even if it's the complete figure.
Edit: hadn't seen the suggestion by tenbobbit, but that reading of the reverse seems to fit the best.
Edited by lrbguy
08/11/2015 11:36 am