Cartier, a rare Art Deco diamond "Montre Bague Navette" keyless ring watch, circa 1920
For a similar ring watch, dated 1920, see "The Magical Art of Cartier", Antiquorum/Tajan, 19th November 1996, lot 122.
For similar examples of watch cases with visible movements dated 1925 and 1921 see, "Le Temps de Cartier", Barraca, Negretti, Nencini, Milan, 1989, plates 114 and 115