It's a Ptolemy, but I have no idea which as I am not an expert on these. The reverse is an eagle standing left on thunderbolt, but that's all the knowledge I have on this type. Here is my only one: PTOLEMY IV AE36 OBVERSE: Diademed head of Zeus Ammon right. REVERSE: PTOLEMIAOU BASILEWS, eagle standing left on thunderbolt, looking back at cornucopiae under right wing Struck at Egypt 221-205 BC 46.4g, 36mm SNG Cop 221
It depends on many factors. First, of course, is condition. Yours and mine are not in the best of conditions. Also, size and weight can make a difference in the value. Do you have the means to weigh and measure your coin? Mine is only 36mm and 46.4g. I've seen some real monsters shown here on this forum. Collectors like the big ones, and the bigger the better.
this may be useful... http://www.megagem.com/ancient/ptolemy_series.html for ptolemy coins...yes ...size really matters. i have a pretty big one.. not the largest, 40mm...but not to shabby.