RIC does not have an issue with only S in left field, it is always paired with F in right field. Perhaps this is an example of a clogged die, though everything else is pretty sharp. Maybe it is only an engraver's error, or maybe it is just an unlisted series. A single example seems more likely to be an error though. I looked in Paolucci and Zub's The Roman Imperial Coinage of Aquileia and Sagramora's MONETA AQVILEIENSIS (294- 452) but neither had anything like this coin. I will, of course, examine it closely when it arrives.
Constantine I
A.D. 320
19mm 3.0gm
CONST-ANTINVS AVG; Helmeted and cuirassed bust right.
VIRTVS-EXERCIT; Standard inscribed VOT/XX with captive seated on ground on either side, S in left field.
in ex. AQP
cf. RIC VII Aquileia 48
