Key to separate Mesembrinellidae from Neotropical Calliphoridae

1 Posterior thoracic spiracle large, reniform, with opening on upper margin and a fringe of long setae (Fig. 7); anterior spiracle small and usually ovate (droplet-shaped), with a more or less broad oval opening above (Fig. 5) or, rarely, with a long, narrow opening gradually widening above (Fig. 6); subscutellum usually from weakly to moderately or (rarely) prominently developed; body color often somewhat testaceous (yellowish or reddish brown), as in Fig. 455; gena usually 1/4–1/2 of eye height; bend of vein M obtuse (Figs 1, 3)........................................................... Mesembrinellidae

- Posterior thoracic spiracle smaller and more circular, closed anteriorly by a larger triangular felt-like lappet and posteriorly by a smaller circular lappet (Rognes 1991: fig. 5); anterior spiracle similar, but opening usually narrower above; subscutellum usually undeveloped or weakly developed; body color usually shiny green, blue, purple or bronze; gena usually about 1/2 eye height; bend of vein M usually acute or right-angled (Fig. 4)........................................ Calliphoridae