How much discussion! The fly is Conioscinella zetterstedti Andersson, 1966 (= C. brachyptera auctt. nec Zetterstedt). "Backen" normally means cheeks, but several Acalyptratae in addition have "Wangen", for example Agromyzidae. Wangen are the prolongation of the strips at the side of the face (antennal pits) along the whole lower part of the eye. This difference often is mixed up by well experienced actual dipterists if they measure the width of the "Backen" (genae) in comparison to the height of the eyes. Some manuals, too, do not consider this difference, they only explain "gena". In such families as Agromyzidae you have to be careful to distinguish between Backen (= jowls) and Wangen (= cheeks), and such a measurement has to be called "Backen plus Wangen" (cheeks and jowls together) for example 1/6 height of eye. "Cheeks" never are equipped with setulae.
C. zetterstedti is a very abundant species along the sea but also in dryer inland grassland, partly with normal and partly with short or even without wings. The larvae are phytosaprophagous. The scutellum is very short, in alcohol material you may see 3 or 5 darker longitudinal stripes on the scutum. The scutum (mesonotum) is much more shining than in similar Aphanotrigonum species. In my database I have 145 articles on this fly either as zetterstedti or as brachyptera. Tricimba (= Crassivenula, = Neuropachys) brachyptera (Thalhammer, 1913) is a quite different species (also in dry grassland), as well Aphanotrigonum nigripes brachypterum (Zetterstedt, 1848) and "Myrmemorpha brachyptera Dufour, 1833" (partly treated as a synonym of Elachiptera brevipennis). In the older literature C. brachyptera auctt. has also been treated in the genera Oscinella, Oscinis, Tropidoscinis or Oscinisoma. I add 6 selected articles on this fly, partly with the exact page numbers on which the species is discussed:

Ardö, P. (1957) Studies in the marine shore dune ecosystem with special reference to the dipterous fauna. - Opuscula entomologica Supplementum 14: 1-255; Lund. [En] 140-147 187-189 214-215.

Bährmann, R. (1987) Untersuchungen der Dipterenfauna in natur- und industrienahen Rasenbiotopen Thüringens (DDR) mittels Bodenfallen (Diptera Brachycera). - Deutsche entomologische Zeitschrift (neue Folge) 34 (1-3): 85-105; Berlin. [De en]. Studies on the fauna of Diptera in natural and industry-influenced grassland biotopes of Thuringia (GDR) by pitfall trapping.

Brauns, A. (1938) Die Flügelrückbildung bei der Strandfliege Conioscinella brachyptera Zett. (Diptera; Chloropidae) und die Beziehungen zur Ausbildung der Flügelsinneskuppeln. - Zoologischer Anzeiger 123 (10-12): 281-295; Leipzig. [De] (Wing reduction in the beach fly Conioscinella brachyptera Zett. (Diptera; Chloropidae) and the relations to the formation of the sense buds on the wings).

Brauns, A. (1939) Morphologische und physiologische Untersuchungen zum Halterenproblem unter besonderer Berücksichtigung brachypterer Arten. - Zoologische Jahrbücher, Abteilung für allgemeine Zoologie und Physiologie der Tiere 59: 245-390; Jena. [De] (Morphological and physiological studies on the halter problem, with special reference to brachypterous species). 248 324-333 341 349 351 370-373 381 383.

Mohrig, W. (1967) Beitrag zur Ökologie und Verbreitung brachypterer Dipteren in norddeutschen Biotopen. - Deutsche entomologische Zeitschrift (neue Folge) 14 (1-2): 169-184; Berlin. [De de] (Contribution to the ecology and distribution of brachypterous Diptera in biotopes of northern Germany).173-176 182.

Wheeler, T. A. (1994) Conioscinella zetterstedti Andersson (Diptera: Chloropidae), a chloropid fly with polymorphic wing reduction, new to the Nearctic and central Palaearctic regions. - Canadian Entomologist 126: 1377-1381; Ottawa. [En en fr]

Dr. Michael von Tschirnhaus