Helike, Achaia, Peloponnesos, AE 23 Dichalkon, 2.98 g, early 4th century, before 373. 

ELIK, Diademed head of Poseidon Helikonios right, within circular 
border of waves breaking. 
Trident between two dolphins swimming upwards; all within laurel wreath with ties at the bottom. 

Lambros p. 16 and pl. 1, 15. Traité 831. 

ex BCD collection. 
The two other examples are in Berlin, found by archaeologists in 1861 in the ruins of Bura, which was severely damaged by an earthquake in 373.

With permission of LHS Numismatik AG, auction 96, May 2006, lot 497.
Sold for 12,500 Swiss Francs.