First, let me say what an enviable coin you have, both for the
portrait and for the iconography of the
reverse.
Propylaeus (propylaios) means 'of or at the gateway'. Bravo for
Google getting the famous one, the herm (copy in Istambul Museum) by Alkamenes, the pupil of Pheidias, of
Hermes Propylaios which stood in
Athens itself, presumably in the Propylaia to the Acropolis.
But here we have an Anatolian
Apollo as a city guardian, and that is wonderful. Maybe the
Apollo Archer reverses at cities in
Thrace are guardian rather than
hunter figures of
Apollo, too? I guess that's a flying cape, very much
stylized?
Head, HN, p. 707, mentions this
type for
Apollo at
Cremna, and says nothing limiting it to Valerian. I bet the
BMC has it. I don't usually recommend anyone's wallowing around in A B Cook's
Zeus (multi-volumed), which does go off on what seem to be tangents, in spite of formidable learning, but I bet you could find something somewhere in it.
Pat Lawrence