John Melville Jones, in "Dictionary of Ancient Roman Coins", writes that the female head on this coin is likely "that of the personification of Macedonia, where Plancius had spent part of his career".
Ex. Classical Numismatic Group, Electronic Auction 358, 2015.
Roman Republic
L. Plautius Plancus (55 BC), Denarius 55, Rome mint
Obverse: head of Diana Planciana to right, wearing petasus
CN PLANCIVS AED CVR S C
Reverse: Cretan ibex standing to right, bow and quiver behind
Weight 3.9 g