A spectacular acquisition!
I know of two other specimens of this
medallion:
(1) In
ANS, ex
Newell Coll.; ex Naville X, 1926, 1765; ex
Hirsch 29, 1910,
Herzfelder Coll., 1221; ex Sotheby, 29 June 1893, Hermann
Weber Coll., 230; doubtless ex Northwick Sale, 1860, 333 (description only). Published by
Toynbee,
Roman Medallions, p. 85, note 103 and
Fagerlie,
ANS Medallions,
Museum Notes 15, 1969, p. 82.
From the same dies as yours, 55.14g, and also bimetallic according to the Naville X
catalogue, though
Fagerlie fails to mention this fact and it's not clear one way or the other from the photographs.
(2) In
Paris according to
Gnecchi no. 21, 50.0g, not illustrated, no mention of bimetallic, but personal examination would be needed to be sure!