Ever since my earlier post, I’ve been rather fascinated with this little remembered myth. The gem is rich in narrative identifying iconography. Peacock = Hera, Io = Bull, caduceus = hermes, BUT what’s up with the harpa?! Seems a borrowing from the Jason myth…
I can’t tell from this image if Argos is janiform or or if his body is shown covered in eyes. Not sure its ancient any way. If it is, it seems rather late Roman.
Liv Mariah Yarrow 
I believe the harpa is an attribute of Saturn…at least on the coins. Given the other deities to which the engraver is alluding, that might not be outside the realm of possibility here. But what do you think is between the bull and the caduceus (the trunk from which the branch on which the peacock perches?)?
Yes, I read it the same, as the trunk from which the branch on which the peacock perches. It usually is Saturn, but also the tool Perseus uses along with Mercury’s shoes to defeat Medusa and rescue Andromeda…