This is Pyrgotid Fly #1.

Mississippi was quite the location for Pyrgotid flies last April: I was able to photograph three different species in 24 hours.

Today I'm posting two. This one is surely Pyrgota undata. The other (Fly #2, which I will post in a moment) looks similar, but I don't think it is P. undata.

Another question about these two flies: both are female? Quoting George Steyskal, in Pyrgotidae the abdomen is "usually elongated," and in the female "segment 7 sometimes longer than the rest of abdomen."

A more detailed look at the head and the tip of the abdomen, with comparison shots of a very similar fly photographed at the same time, are here: