Watch List notes:

Burgundians or Franks in Gallia (?). AV Tremissis, in the name of Valentinian III, 451 AD and later. D/ DN PLA VALENT-I-NIANVS F (sic) AVG. Pearl-diademed, draped and cuirassed bust right. R/ Cross potent within wreath; below, COMOB. Cf. RIC X, 3784. Cf. Wroth 4 (Vandals, Gaiseric). AV. g. 1.43 mm. 14.50 RR. Very rare. VF/Good VF.

A conjectural attribution, on grounds of style, smooth (but not small) head and obverse legend.