Watch List notes:

ABBASID: al-Mahdi, 775-785, AR dirham (3.00g), al-Yamama, AH168, A-215.1, citing the governor 'Abd Allah b. Sa'id, with an extra letter after the name Sa'id, some light hornsilver on the obverse, VF, RR. Al-Yamama was the first mint in Arabia to strike silver coins, located near the modern city of Riyadh, with its administrative capital at the town of Hajar. It operated AH165-170.

Estimate: 400-500 USD