This coin seems to be an unofficial coin or maybe it is just plain sloppy engraving. The mintmark, which should be SMKB, has an X (or an odd K) instead of an M. The Vandals also minted this type, but they are usually a bit more crude.
Theodosius II
A.D. 423- 425
12x13mm 1.3gm
DN THEODO-SIVS PF AVG; pearl diademed, draped and cuirassed bust.
REV: Cross in wreath.
In ex. SXKB
Cf. RIC X Cyzicus 449
