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The Systema Dipterorum suggestion that Gymnopa rufitarsis Meigen 1838 is a synonym of Parydra coarctata (Fallén) is an error. Mathis and Zatwarnicki (1995) list Ephydra rufitarsis Macquart 1835 as a synonym of P. coarctata, but make no mention of Gymnopa rufitarsis Meigen anywhere in their Catalog, or in later updates of the catalogue.
On the New Diptera Site, Gymnopa rufitarsis Meigen is given as a synonym of Madiza rufitarsis Mg., itself a synonym of Madiza glabra. (See https://portal.cy...3/synonymy )
Gymnopa is now regarded as a synonym of Mosillus, an ephydrid that superficially looks rather like Madiza, and would explain why Meigen thought his rufitarsis was a Gymnopa. I am quite certain that Bezzi was (correctly) thinking of Meigen’s rufitarsis when he labelled the specimen.