Licinius II or Constantine II. Perhaps some other obscure ruler, but I know those two had small busts issued. I'm ugessing Licinius II (Constantine II was a bit later than this reverse type).
Heres what I think it is:

Attribution: RIC VII: 11 Cyzicus (R3)
Date: 317-324 AD
Obverse: DN VAL LICIN LICINVS NOB C, small laurate
bust lt., imperial mantle
Reverse: IOVI CONSERVATORI CAESS, SMK in ex., wreath
in lt. field and gamma in rt. Field
Heres what I think it is:

Attribution: RIC VII: 11 Cyzicus (R3)
Date: 317-324 AD
Obverse: DN VAL LICIN LICINVS NOB C, small laurate
bust lt., imperial mantle
Reverse: IOVI CONSERVATORI CAESS, SMK in ex., wreath
in lt. field and gamma in rt. Field






















