The Tetras denomination
The Tetras was a bronze denomination within the Sicilian Greek system corresponding to 4 onkia - or one third of a Litra.

The tetras was denoted by four pellets on the reverse.
Tetras

(1) Akragas 425-406 BC
Obverse: eagle right, tearing at hare AKP_A
Reverse: Crab, crayfish left below •••
Ref: SNG COP. 75 var. SNG München 132