This variant not noted by the usually sharp-eyed
Cohen.
No mention of it on
denarii in
BMC, and the two illustrated specimens indeed omit the
sphinx.
BM 108,
sestertius, pl. 108.7, however, notes the
sphinx in a footnote:"Arm-rest on
rev. shaped like
sphinx (?)."
No mention of the
sphinx in the brief discussion of this
type in Kaiser-Raiss' dissertation on Commodus' coins, p. 39.
I indistinctly recall noting the
sphinx on
denarii before; maybe I wrote it into my
BMC that I lost to bagsnatchers in 1999! Or maybe I just noted it on another
sestertius like BM 108.
I don't know whether this detail has ever been noted and discussed in the scholarly literature; I rather suspect not.
Your point about the globe is a
good one and deserves following up!