English silver verge watch with extremely rare movement Circa 1750

Silver and tortoiseshell watch decorated with stones
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A verge watch with extremely rare movement made by James Rousseau in London, England, circa 1750. Both cases of this open faced watch were made later especially for the movement. The enamel dial has Roman hour numerals, outer Arabic five minute numerals and fine steel hands. The movement of greatest rarity has silver decorations, is set with stones and the cock and pillars are probably all with tourmalines.
The movement is signed.
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Diameter: 50 mm
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Weight: 97 g
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Signed: Ja. Rousseau London
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A comparable verge movement from this period with such decoration doesn’t appear to exist. Therefore, it seems possible that this is a unique piece. Unfortunately, the original, possibly precious case has disappeared.