The present volume treats four small families of aquatic beetles belonging to the so-called Coleoptera Adephaga, viz., Gyrinidae (whirligig beetles), Haliplidae (crawling water-beetles), Hygrobiidae (squeaker beetles) and Noteridae (burrowing water-beetles).
The Danish and Fennoscandian faunas of these families comprise 13 species of Gyrinidae, 21 species of Haliplidae and 2 species of Noteridae, making a total of 36 species. All North European species of the four families are included, adding a further 3 species of Gyrinidae, 1 species of Hygrobiidae and 1 species of Haliplidae. The Aquatic Adephaga (Coleoptera) of Fennoscandia and Denmark, Volume 1 starts with keys to the Fennoscandian families of Adephaga for both adults and larvae. General information on morphology, zoogeography and bionomics is given under each family.
The keys and descriptions have generally been kept rather long, allowing the use of as many diagnostic characters as possible, many species being difficult to separate without examination of male and/or female genital sclerites.
The keys and the descriptions of species are only sufficient for the separation of North European species, but the remaining sections treat the families on a world basis. Some revisional work has been included. The following two new synonymies have been established: Haliplus apicalis Thomson = H. strigatus Roberts, and H. lineoIatus Mannerheim = H. schaumi Solsky. Lectotypes have been designated for the following species: Dytiscus impressus Fabricius, Haliplus affinis Stephens, H. sibiricus Motschulsky, H. schaumi Solsky, H. nomax Balfour-Browne, H. browneanus Sharp, and H. interjectus Lindberg.