Key to the species of Grzegorzekia (female of G. bushyae unknown)

1 Abdominal tergites of both sexes with narrow pale posterior bands (as Fig. 1); male mid-tibial organ present (as Fig. 6); female sternite 8 longitudinally divided medially (Figs. 11–12); (western Nearctic)....................................... 2

- Abdominal tergites without pale posterior bands, but tergites may sometimes have anterolateral pale areas on some or all of tergites 2–7; male mid-tibial organ absent; female sternite 8 undivided medially in known species (female of G. bushyae unknown) though may have an emargination posteromedially (as Fig. 10); (Palearctic, Holarctic)........................ 3

2 Male terminalia as in Figs. 3–5; cercus without a strong, black, spine-like seta; gonocoxal comb of black spine-like setae visible in dorsal view (Fig. 5; com); gonocoxal lobe slender, elongate with apical setae (Figs. 3–4; gc lb); female sternite 8 posteromedially lobate in ventral view (Fig. 11); ( western Nearctic).................................. .. G. kerri Fitzgerald n. sp .

- Male terminalia as in Figs. 7–9; cerci each with a single, strong, black spine-like seta; gonocoxal comb of black spine-like setae not visible in dorsal view; gonocoxal lobe short, cow-horn-like, without apical setae (Figs. 7–9; gc lb); female sternite 8 without distinct posteromedian lobes in ventral view (Fig. 12) (western Nearctic).................... G. quercus Fitzgerald n. sp.

3 In lateral view, gonocoxites (section II) with a single apical lobe bearing a comb of stout, black, spine-like setae (as in Fig. 4; gc II); female unknown; (England, France).................................................. G. bushyae Chandler

- In lateral view, gonocoxites (section II) with two lobes, the anterior lobe bearing a comb of stout, black, spine-like setae (as in Chandler, 1999; Fig. 13); (Palearctic and Holarctic).......................................................... 4

4 Aedeagus slender, nearly parallel-sided, elongate, extending beyond apex of gonocoxites; female with sternite 8 not deeply emarginated medially, posterior edge medially lacking stout, black, spine-like setae (see Papp & Ševčík, 2007, Figs. 1–5); (Hungary, Slovakia)............................................................. G. hungarica Papp & Ševčík

- Aedeagus triangular, shorter, not reaching apex of gonocoxites (see Chandler, 1999, Figs. 13 –14); female with sternite 8 posteromedially more deeply emarginated, with two patches of stout, black, spine-like setae (one patch on each side of the median emargination with each patch bearing 2–3 setae) as Fig. 10; (Holarctic)........................... G. collaris (Meigen)