Watch List notes:

MYSIA, Uncertain (Atarnios?). 4th century BC. Æ (11mm, 1.25 g, 12h). Crested Corinthian helmet left / Serpent coiled left; ΘE monogram within coil. SNG Arikantürk 1218 var. (serpent right). Green patina, light earthen dusting. VF. Well centered. Very rare.

See CNG 66, lot 651, for a similar issue in silver, but with Herakles on the obverse.