Doug:
Your coin has all the hallmarks of having been
engraved by Sellwood's engraver C as identified in
his classic die study [
Sellwood, D. 1976. The Drachms of the
Parthian "Dark Age". Journal of the Royal Asiatic Society, 1976 (1): 2-25.].
He generally characterizes engraver C's
reverse style as: "
Head in correct proportion but tending to jut forward.
Bashlik cheekflap runs down parallel to upper
arm, often reaching to elbow. Single diadem end converging with
bashlik neckflap above throne.
Arm definitely crooked at elbow on early issues but tending to become straight and horizontal with later ones. Sleeve ends in horizontal
bar and extends almost to ground. Left thigh curves towards knee, and
leg set back at 45°. Boot lace ends exaggerated and divergent. Throne back finishes at shoulder level or higher. Throne legs have three or four bulbs of even size, irregularly spaced. Ground line under archer's feet only and slopes markedly upwards to right. Omicron is small on early issues and pellet-shaped on later ones."
And specifically for the
Type 33 drachms
Sellwood adds: "Engraver C consistently mis-spells ΘΕΟΠΑΤΟΡΟΣ as ΘΕΟΠΑΤΡΟΥ." Your coin does indeed read ΘΕΟΠΑΤΡΟΥ.
Sellwood claims that engraver C was involved in engraving examples of
Types 26, 27, 28, 29, 33, 31, and 34 drachms.
I can email you Sellwood's paper if you don't have access to it.
Mike