Mantinea, Arkadia, AR triobol. ca 490-480 BC. 2.98 g. 

Bear walking left on dotted groundline, countermark 
of star on shoulder.
M-A, dolphin swimming right within a dotted square, all 
within an incuse square. 

Jameson 1261 (this coin), BMFA 1259, SNG Fitz. 3881. 

With permission of Stack's auctions, Jan. 2008.

Extremely rare. 
Estimate £100.