Constans. 337-350 AD. Æ 36mm -- Medallion (31.20 gm). 

CONSTANS PF AVG, pearl-diademed, draped and cuirassed bust right.
VIRTVS AVG, Constans standing right, holding transverse spear and globe; captive seated right at feet.

Gnecchi 23 and pl. 135, 8; Cohen 180. 
Very rare! .

Ex-Cornelius Vermeule III Collection. Ex Edward Gans collection.

CNG (trading as Historical Coins) on ebay, Aug. 1999. Item no. 715579