OK...I found this in my research:

The coin is a 'stater' = tetrdrachm an Ancient Greek silver coin equivalent to four drachmae. It was in wide circulation from 510 to 38 BC.

The figure on the left is Athena wearing a crested Corinthian helmet ornamented with a coiled snake, her braided hair falling straight down the back of her neck and visible as wavy locks beneath her helmet to the side. 

On the right is a figure that could be Nike holding a wreath and ship stylis (ornament) or a mast or perhaps it's Hermes. 

Below the wreath there's a mint control mark consisting of the Greek letters 'iota, delta, iota' under Athena's right wing, and to the right the inscription "Of Alexander."?