As above, it's a bronze coin of emperor Severus Alexander. Its obverse inscription reads IMP CAES M AVR SEV ALEXANDER AVG. Assuming that's a sestertius (that's why we request that people who post questions asking for coin identification provide diameter in mm and weight in g), the reverse reads P M TR P COS P P and depicts Salus seated left, resting elbow on chair and feeding from patera a serpent rising from altar. Some references: RIC IV 393; BMCRE 39; Banti 61.
