This coin is interesting because Constans is called junior (IVN) when there was obviously not a Constans Sr. The only coins that should have IVN at this time are those of Constantine II and from a few years earlier Licinius II. This was surely a misunderstanding on the part of the engravers which was quickly fixed. In RIC VII, Bruun says that this "is merely a curious contamination at an early stage..." (RIC VII pg 31)
Constans
A.D. 333- 336
CONSTANS IVN NOB C; laureate, cuirassed and draped bust.
GLOR-IA EXERC-ITVS; Two soldiers helmeted, stg. facing one another, reversed spear in outer hands, inner hands on shields resting on the ground; between them two standards.
in ex. SMHA✶
RIC VII Heraclea 139