Seleukid Kings, Seleukos II, AE19. Nisibis mint. 246-225 BC. 

Obv: Heads of the Dioskuri right, each wearing a pileus.
Rev: BASILEWS SELEUKOU above and below the Dioskuri on horseback riding right.

SC 760; WSM 827. Rare.

Courtesy of TimeLine Originals (www.time-lines.co.uk), Jul, 2010

(with thanks to "Lloyd T" on the forvm for identifying this
rare coin with the following addition:

SC records this type in a 2.62-2.80 gm module of around 15 
mm diameter, but notes the existence of 2 specimens in the 
Afyon Museum weighing 3.06 and 4.51 gm suggesting the 
existence of a larger denomination of the type. This coin  
appears to be representative of the latter. Newell 
cataloged one example of the type weighing 2.615 gm in the 
Imhoof-Blumer collection.
Nice coin and apparently quite rare.