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My immediate impression is Xenochaetina. Notice the hairs along Rs and R4+5, the source of the genus name. But I am not good with Lauxaniidae and I have not tried to run your fly through the key.

There is a key to New World genera of Lauxaniidae in Manual of Central American Diptera volume 2. Steve Gaimari, one of the authors, is one of the earliest members of diptera.info. http://www.dipter...?lookup=55