A short biography of Oscar Ringdahl (1885-1966) is given together with a complete bibliography of his zoological papers. He published 258 new specific or subspecific names and described 43 new genera or subgenera within Diptera Brachycera, especially in the families Muscidae, Anthomyiidae, Tachinidae, Scatophagidae, Syrphidae and Dolichopodidae. At present about 185 of these names are considered to be valid. A list of the taxa named by Ringdahl and their present status is given.
The Scatopsidae in Zetterstedt's collections have been revised. Lectotypes for the following taxa are designated: Scatopse geniculata Zett., 1850=Reichertella geniculata (Zett.); S. flavitarsis Zett., 1850=Coboldia fuscipes (Meig.); S. albitarsis Zett., 1850=Holoplagia albitarsis (Zett.) and Aspistes nigripes Zett., 1860=Anapausis nigripes (Zett.), syn: A. palustris Edwards, 1925, n.syn.
Glabellula arctica (Zett.) is recorded from three Swedish provinces as an ant guest, living in the nests of four Formica species. Some details of the behaviour of the adult and the larva are described as well as the morphology of the last larval instar, the pupa and the malc and fcmale abdomina. The systematic position of the species is discussed.
Lectotypes are designated for Cordylura dentimana Zetterstedt, 1838, Cordylura fulvipes Zetterstedt, 1838, Cosmetopus bergrothi Becker, 1900, and Cosmetopus simplicipes Becker, 1900. C. fulvipes Zett. is found to be a synonym of C. dentimana Zett. (n. syn.). The opinion that C. bergrothi is a synonym of Cosmetopus longus (Walker, 1849) and that C. simplicipes Beck. should be treated in a separate genus, Pleurochaetella Vockeroth, is confirmed. Cosmetopus ringdahli n. sp. is described and figured on material from Sweden and Finland. Distinctive characters of the other species are discussed and partly figured.
A new species, Themira biloba n. sp., closely related to Themira putris L., is described and figured on material from the shore of a small eutrophic lake in South Sweden. Comparable characters of Th. putris are also figured.
The type series of the Sphaerophoria species described by J. W. Zetterstedt have been examined and lectotypes designated. It has been confirmed that S. nigricoxa Zett. is a synonym of S. scripta L. and that S. flavicauda Zett. and S. nitidicollis Zett. are synonyms of S. rueppelli Wied. S. loewi Zett., S. dubia Zett., and S. abbreviata Zett. are good species. The descriptions of S. multipunctata Zett. and S. insignita Zett. are based on single abnormal females. With our present knowledge of Sphaerophoria females, they cannot be interpreted. S. sarmatica Bankowska is a synonym of S. dubia Zett. (n. syn.).
Some cases of "melanoid females" of the genera Platycheirus, Melanostoma, and Sphaerophoria are described and figured. All specimens show drastic abnormalities in the genital segments. Most obvious is a ring-shaped fusion of sternite and tergite in segment 7 which fusion is present in all the I3 specimens studied.