Gordian III, AE23 of Anchialus, Thrace. 23.4mm 6.6 gr. 

AVT K M ANT GORDIANOC AVG, laureate head right.
AGXIALEWN, Poseidon, naked, standing half right, foot on 
rock or prow, holding trident and dolphin.

AMNG 513 var (this reverse for Caracalla); cf Varbanov 658 (unclear reverse). Apparently unpublished (not in Varbanov, Moushmov, Mionnet, BMC, AMNG etc.).

Collection of Kevin Neve, Dec. 2012