Neat coin, and I
hope that it is genuine but it has a few indications that it
could be fake - for one it looks to be nearly perfectly round, which most ancient coins are not. The details seem to be lacking too, but it is not possible to say it is fake based on just those two factors.
I would suggest sending it to David Sear, widely acknowledged as "the" expert in ancient Greek coins (he has authored several books on them) the fee for a basic certification is $40, well worth it if the coin turns out to be genuine but would feel like forty bucks lost if it is fake. Here is the website:
http://www.davidrsear.com/certification.html
Mr Sear also offers a detailed certification for $50.
I would say Baktria too, my eyes are not good enough to make out all the letters but on the reverse the letters
"BASILEUS" (in greek letters of course not English) means "king" or "lord" and on the obverse to the right of the head is likely the name of the ruler, in this case honoring the deceased Diodotus but many possibilities - the reverse does seem to have the name "AGATHOKLES" but your coin is missing either an "O" or the "theta" which is an "O" with a bar in the center. Missing a letter or mis-spelling is not
too unusual for ancient coins but is another possible red flag.
One more
possible "
red flag" is that the lettering on the obverse is in straight parallel lines running vertically on the coin, like many other Greek coins but unlike most Baktrian types which have the lettering running around the rim if they have lettering on the obverse at all. You can browse the images on Wildwinds.com, the link for Baktrian kings is
http://www.wildwinds.com/coins/greece/baktria/t.html unfortunately Wildwinds does not filter out fakes, just copying the images posted in various online auctions and sales so among the genuine images are mixed a few frauds. (I don't blame Wildwinds for this, fakes have been a problem with ancient coins for many years and in some cases it takes an expert to tell the difference.) There are many variants of Baktrian coins so your coin might be an unusual example that does not quite match the photos online.
If it were my coin I would pack it up and send it off to David Sear to have it examined and certified. I do hope it turns out to be genuine.
Good luck and good hunting amigos, I hope you all find the treasures that you seek.
Oroblanco