This one appeared in a lot by a british dealer.
CONSTANTIUS II AE2 21mm 4g Centenionalis/Maiorina (aVF, patina)
AV: DN CONSTAN - TIVS PF AVG; pearl-diademed draped cuirassed bust r.
REV: FEL TEMP RE - PARATIO; roman soldier spearing fallen enemy, bear-headed.
EXE: AMB, Ambianum mint.
REF: RIC VIII Ambianum 48, rated as C (but very scarce) August - late 353AD.
Very scarce mint for Constantius II. The mint at Ambianum was opened by Magnentius and was closed soon after his total defeat and the city entering Constantius II's authority. This type was minted for a brief period from August 353 until the mint was closed before the end of the year.