De Nederlandse soorten van het genus Cercyon leach (Coleoptera: Hydrophilidae)

The distribution of the genus Cercyon Leach in the Netherlands has been examined. A survey of characters and character-states is provided. Keys to species and supraspecific taxa are given. The distribution of each species is mapped and the male genitalia are figured. It is noted that the presence or absence of an emargination at the apex of the prosternum is an important character in the supraspecific classification of the genus Cercyon. The presence of male adherence discs at the maxillae is not unique for the tribe Cercyonini, but occurs also in the tribes Sphaeridiini and Megasternini. C. laminatus Sharp is placed in the subgenus Paracycreon d'Orchymont. C. alni Vogt is placed in synonymy with C. convexiusculus Stephens. A lectotype is designated for Sphaeridium ferrugineum Fabricius. This species belongs to the genus Leiodes Latreille. Although the same Cercyon-species occur in dung-samples from the Netherlands, England and Finland, considerable differences in the quantitative species-composition exist. In the last decades C. atricapillus (Marsham) has become very scarce in the Netherlands. Most specimens of Cercyon were collected during spring, except C. laminatus and C. atricapillus, which were more abundant during summer.