pdf file - way over my head - a technical paper that revises the Empidoidea. However, I thought that it might be useful for Bug Guide as there is an illustrated key to the families and some of the genera of these flies. All of the figures/illustrations are at the end of this paper after the references.

"...All morphological characters are extensively discussed and illustrated, including details of the
antennae, mouthparts, internal thoracic structures, wings, and male and female terminalia. In
addition, a key to families and unplaced genus groups of the Empidoidea is provided. Feeding
habits are also discussed in terms of the empidoid ground plan condition".