This is a fairly rare type first minted under the authority of Vetranio (Siscia 293), but also struck two other times, when Gallus (Siscia 355) and then Julian II (Siscia 386) became Caesar. We can't be certain that this type was even struck for Constantius II each time, but we have to assume they were; and accordingly, this coin has three RIC numbers.
Constantius II
circa A.D. 350
DN CONSTANTIVS PF AVG, pearl-diademed, draped and cuirassed bust.
GLORIA ROMANORVM, Emperor, bare-headed and in military dress, stg. facing, head l., holding standard with Chi-Rho on the banner, and spear.
In ex. ASIS
RIC VIII Siscia 293, 355, 386
