This coin looks like RIC 103 except there is no evidence of a star in the mintmark. RIC does not list this issue, but Ferrando has examples for Constantius II (#1142) so not surprising to find one for Constans.
Constans
A.D. 348- 350
21x24mm 5.5gm
D N CONSTANS P F AVG; pearl diademed, draped & cuirassed bust right.
FEL TEMP R-EPARATIO; Soldier spearing fallen horseman.
In ex. SARL
RIC VIII Arles -- ; Ferrando --