This coin is a variation on the regular bust type because it looks like it is facing, with head right. Several other examples on Lech’s page--
http://www.notinric.lechstepniewski.info/7nic159v.htmlHelena
A.D. 325- 326
18mm 2.1g
FL HELENA AVGVSTA; diademed and draped facing, head right.
SECVRITAS REIPVBLICE; Securitas standing left, holding branch pointing down, raising robe with r. hand.
in ex. SMNΓ
cf. RIC VII Nicomedia 159