This female Black Darter Sympetrum danae is clearly showing the characteristic yellow splash pattern on the side of the thorax seen in both the male and female. She does however have a far stockier body than that of the male seen below and she also has a clearly visible prominent vulvar scale on the underside at the end of the abdomen.
The photo below clearly shows the 2 side stripes on the thorax of this male Common Darter Sympetrum striolatum. Also visible is the light yellow stripe running down the legs.
And finally, not a darter, but another later summer species Emerald Damselfly Lestes sponsa- and not just 1 but a pair of pairs!