Head of a nymph to left, wearing a sakkos adorned with a central band and circular earring // Quadripartite incuse square. 11mm, 1.36 grams. Rosen 596-597 var. SNG von Aulock 1813-1815

This denomination is variously referred to as "trihemiobol", "diobol" or "hemihekte". 

From an old US collection, ex-CNG.

Phocaea or Phokaia was an ancient Ionian Greek city on the western coast of Anatolia. Greek colonists from Phocaea founded the colony of Massalia (modern-day Marseille, in France) in 600 BC, Emporion (modern-day Empúries, in Catalonia, Spain) in 575 BC and Elea (modern-day Velia, in Campania, Italy) in 540 BC.