Size estimated (body length). There were many shed skins and a few adults in an old field adjacent to woodlands. The adults present all seem to have deformed wings, which likely accounts for them hanging around in the afternoon. A few were singing from adjacent woodlands.
The couple of individuals I photographed sure look like Magicicada tredecassini Alexander and Moore 1962. I don't see any substantial orange behind the eye, and the abdomens are completely dark. They also seemed on the small side to me. Comments?
(Update: also, listening to the songs on the magicicada.org web site, they match Magicicada tredecassini. Seems this is good enough to move to species level--about as certain as we will get with this genus.)

See also this series of nearby individuals: