Acalyptratae is a subsection of Schizophora, commonly referred to as the acalyptrate muscoids (or simply acalpytrates). It is a very large assemblage, exhibiting very diverse habits. The name refers to the lack of calypters in the members of this group of flies.
Links: Diptera classification
Does someone has a scan of Nartshuk E.P. 2003. Key to families of Diptera (Insecta) of the fauna of Russian and adjacent countries. Proceedings of the Zoological Institute Vol. 294: 1-252 for me?