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June 08, 2010, Naro-Fominsk, Moscow region, Russia. On and near a dead fallen aspen (same location as for Pseudoseioptera demonstrans). Numerous males (wing length 7 to 9.5 mm) and a single female (wing length 8.5 mm) were observed and collected. Very characteristic appearance, with glossy-black body, darkened wings, yellow halteres, yellow patch in upper part of pleurae (in the field looks much like a second pair of halteres), and greyish-tomentose lower part of pleurae, coxae, and trochanters. Yet a closer look revealed that some males have wings more clear while others are with strongly infuscated wings. Examination of genitalia showed that males with more clear wings are Gnophomyia viridipennis, and those with strongly infuscated wings are Gnophomyia acheron (described from East Palaearctic, recorded from the Russian Far East and West Siberia, in West Palaearctic at least from Finland in Stary & Salmela, 2004; I don't know if it's known from European Russia). There's probably a third species, too, more common G. lugubris, very similar to viridipennis, so further examination of location/genitalia of collected specimens is needed.
Here's what I believe to be G. viridipennis.

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And here's what I believe to be G. acheron (of course it's almost impossible to judge how dark the wings are when they are folded like this, I'm based mostly on less yellow, rather whitish halteres).

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The wings: top - G. viridipennis, bottom - G. acheron. Hancock (2008a) says that they can be separated by the lack of stigma in acheron, yet I would say that, at least in this specimen, faint yellowish stigma is present. Additionally, vein rq in acheron seems to have more proximal position (closer to the point of furcation of veins r2 and r3), and vein m-cu located more distally; and maybe in viridipennis vein a2 is somewhat curved inwards when reaching the wing margin. Male genitalia and, hopefully, report of new information later.

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Male genitalia, top: G. acheron, bottom: G. viridipennis.

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Nice series:)