From the introduction:
The present volume of Fauna Entomologica Scandinavica is a direct continuation of volume 3 of this series, which appeared in 1975 and dealt with the subfamily Tachydromiinae of the "Empididae". However, when compared with the preceding tachydromiine part, the present volume will be seen to differ in two important and closely-linked aspects – the title and the rather detailed General part. One new feature of this volume is the division of the former "Empididae" into four distinct families. This has given rise to the superfamily name Empidoidea in the title and to the detailed General part which, I hope, provides adequate evidence for the proposed new classification, based on the comparative holomorphological method, and for the presumed phylogeny of the 'higher' Brachycera.
The present volume covers the Scandinavian species of the former Ocydromioinea-group of subfamilies, i.e. the Hybotinae and Ocydromiinae of the Hybotidae (the Tachydromiinae were treated in volume 3 of the series), the Atelestidae, and the Microphoridae.
The material is arranged in the same way as in the 'tachydromiine^ volume. Each species begins with the valid name followed by the original combination; then the synonyms are listed chronologically with their bibliographical references, followed by a short diagnosis and a description to ensure correct differentiation from related species. The distribution in Fennoscandia and Denmark, the general distribution, and the flight-period of each species are briefly outlined, whilst more detailed information on the distribution in Scandinavia and adjacent countries is given in the 'Ctalogue' at the end of the volume. Notes on biology immature stages and habitats of the species are usually summarised in the generic diagnosis. The main diagnostic features for each species are illustrated, including the male genitalia which are often the decisive character for exact identification. As these three families include forms that are morphologically very diverse, each genus begins with a habitus drawing, generally of type-species. Species which might occur in Scandinavia, or species closely related to the known Scandinavian species, are also mentioned and briefly diagnosed. A study of all the available type-material was an essential part of the present work, and new synonymies, lectotype designations, holotype identifications and other notes on type material are given in a separate paragraph.
The families, subfamilies and genera treated are briefly diagnosed, with notes on classification and distribution, and keys for the identification of genera and species are also given. As already mentioned, the General part is rather detailed because of the proposed new classification of the former "Empididae".