Closest I found was a listing on the Wildwinds site that mentioned a mule with a reverse of Severys Alexander. (RIC 100 - "P M TR P VIII : COS II PP" Libertas standing left, holding pileus & sceptre Reka Devnia p137). That doesn't seem to show the altar apparent in the lower left of the reverse though. It's also possible that the previous owner is wrong on the Maximinius ID - the obverse legend is rather blotto. This seems to show the emperor making sacrifice, as seen on several Severys Alexander denarii, but this piece appears to be a Follis.