Possibly Galatian Celts ?

3rd-2nd centuries BC. AR Tetradrachm 32mm 15.8 g.

In the name and types of Alexander III of Macedon. Head of Herakles right, wearing lion skin

/ Zeus Aëtophoros seated left; winged thunderbolt in left field, X in pellet form(?) below throne.

Cf. CNG 90, lot 752; otherwise, unpublished in the standard references.

This coin is part of a series featuring an unusual obverse style and light weight (averaging between 15.5 and 16.5 grams), as well as a variety of symbols 

These issues sometimes also feature an X below the throne -Price B4-. While the light weight and style suggest an origin among the eastern Celts, the consistency of the style and metrology, as well as the good epigraphy suggests a more formally organized mint, unlike definitively Celtic issues that copy Alexanders