Vologases IV, King of Parthia. Edessa mint, ca 147-191 AD. AE Tetrachalkon, 20mm, 6.40 g. 

Diademed bust left, wearing tiara with flap and decorated 
with horn and hooks; B behind.
Large symbol resembling O on reversed T, around, "Volgasi 
Arsak Malka Malkin". 

Sellwood 84.134; Shore 436; BMC Parthia 96-99 (under Vologases III).

With permission of CNG, cngcoins.com, Electronic Auction 187, 2008, lot 63. Sold for $176.