AE 25mm, 13.46 g c. BCE 115-c. 89/88
BMC 13. 18, 61, Sear 3639
O: Mithradates as Perseus wearing a Phrygian helmet
R: Pegasus grazing l. AMIΣOY and two monograms below.
Pegasus was apparently utilized as a symbol on Mithradatic coinage until about BCE 89/88 when the stag became the prominent symbol.
http://press.princeton.edu/titles/8977.html This book is an interesting and even fun read if one overlooks the minor editorial errors that ultimately do not detract from the well told story unless you take them too seriously.