This coin is not listed in RIC for Constantine (only Licinius and Maximinus). It should be RIC VI Nicomedia 70c. It is not as rare as being unlisted would indicate though, as I had another example and have seen a few others.
Constantine I
A.D. 312
23mm 4.7gm
IMP C FL VAL CONSTANTINVS P F AVG; laureate head
VIRTVTI E-XERCITVS; [Valor of the Army] Virtus advancing r. in military dress, r. holding transverse spear, l. shield and trophy over shoulder, A in right field,
In ex. SMN
RIC VI Nicomedia --