Watch List notes:

Hermaios. Ca. 90-70 B.C. AR tetradrachm (26 mm, 9.78 g, 12 h). Lifetime issue. BAΣIΛEΩΣ ΣΩTHPOΣ / EPMAIOY, diademed and draped bust of Hermaios right, wearing helmet adorned with bull's horn and ear / Zeus-Mithra enthroned facing slightly left, holding scepter; monogram to left; Kharoshthi legend around: Maharajasa tratarasa / Heramayasa. Bopearachchi 4D; MIG 412a; SNG ANS 1344-5. Light porosity on obverse. Good very fine. 

The vast bulk of the Hermaios coinage consists of posthumous issues. Lifetime issues, especially the helmeted type like the coin offered here, are quite rare! 

Although the figure on the reverse is normally described as Zeus, it is very clear from the radiate head on this coin that Mithra was intended, or at least a syncretic version of Zeus which encompassed Mithra.