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Oscinisoma cognatum (Meigen, 1830), Chloropidae. The three species O. germanicum (Duda, 1932), O. gilvipes (Loew, 1858), and O. cognatum are extremely difficult to distinguish. The image shows a shining humeral callus (= shoulder), a largely dark gena, a slightly flattened thorax, a wing only slightly longer than the abdomen, a completely yellow hind tibia, a frons darkened aside of the ocellar triangle, an ocellar triangle very long and with pollen (= pubescence) only aside and in front of the ocelli, a triangle not touching the eye margin, about ¾ width of the frons between the eyes, tergites glabrous, wing membrane partly yellowish, R4+5 apically slightly divergent with M1+2. All these characters here observable are not sufficient but typical for a distinction after the unpublished study (of much material including the types of gilvipes and germanicum) by M. von Tschirnhaus.
This is a typical species of the genus Oscinisoma Lioy, 1864 (Chloropidae, Oscinellinae), partly wrongly spelled Oscinosoma. The mesonotum (= scutum) is slightly depressed and not smooth but it has a rough surface.
The adults prefer the stratum close to the soil between Carex tussocks, running ant-like and living together with the raptorious Stilpon spp. (Hybotidae).