In this paper a previously unknown species of the genus Dahlica Enderlein, 1912, from the subgenus Postsolenobia Meier, 1957, is described as Dahlica (Postsolenobia) weidlichi sp. nov. and compared with the already known species of this subgenus. Analysis of DNA barcodes for all five validly described taxa of the subgenus Postsolenobia show an unexpected pattern of genetic diversity. Careful re-examination of morphological traits fully supports this pattern and leads to the description of a new species. In addition, the habitat of the new species is characterised and the entire distribution of the subgenus is discussed.