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I did some research. In Mihalyi Taxigramma is split into three genera Taxigramma sensu stricto (includes heteroneurum), Hilarella (that includes hilarella and stictica) and Paragusia (that include eleganula and multipunctata). Now Taxigramma (sensu stricto) has a distinctive feature, its wing venation is pushed towards the wing base leaving most of the wings essentially void of closed cells, and covered mostly by extensions of the venation. THis is well visible in the first pic, therefore I think this is heteroneurum. The description also fits, and it is also mentioned that this is a fly found in sandy habitats. So I think this is Taxigramma heteroneurum. Maybe heteroneurum points to this strange wing venation pattern.