Countermark

https://rpc.ashmus.ox.ac.uk/countermark/320 
GIC 193
gorgoneion
circular 
The gorgoneion is presumably that on the breastplate of Athena Ilias 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC I, 2312 Show 2312 7 1
RPC I, 2313 Show 2313 5 1
RPC I, 2314 Show 2314 10 1
RPC I, 2316 Show 2316 5 1
RPC I, 2316 Show 2316 11 1
RPC I, 2317 Show 2317 2 1
RPC I, 2317 Show 2317 3 1
RPC I, 2317 Show 2317 4 1
RPC I, 2318 Show 2318 3 1
RPC I, 2317 Show 2317 7 1
RPC I, 2313 Show 2313 16 1
RPC I, 2318 Show 2318 2 1
RPC I, 2316 Show 2316 19 1
RPC I, 2316 Show 2316 3 1