Revision of the Palaearctic species of the Helophorus minutus group (Coleoptera: Hydrophilidae), with chromosome analysis and hybridization experiments

. Investigation of the chromosomes has revealed a Helophorus species from Central and Eastern Europe, and West Siberia, here described as H.paraminutus sp.n., which often closely resembles minutus F., though some specimens are larger and resemble lapponicus Thomson. The chromosomes of paraminutus are clearly distinct from those of minutus but closely resemble those of lapponicus. In the laboratory first generation hybrids were obtained between minutus and paraminutus, lapponicus and paraminutus, and lapponicus and minutus, but in no case was it possible to breed from these hybrids. Thus there can be no doubt that these three species are distinct. Recognition of paraminutus as a distinct species, despite the fact that study of its morphology alone could suggest introgressive hybridization between lapponicus and minutus, requires the recognition of limbatus Motschulsky as a species separate from H. lapponicus and necessitates the revision of the Helophorus minutus group of species which, as here defined, includes minutus, paraminutus, hilaris Sharp, lapponicus, limbatus, mervensis Semenov, rinki Angus, fulgidicol‐lis Motschulsky and asturiensis Kuwert. Types and synonymies are discussed, and a key to these species given. Two old, imperfectly known, names are discussed to clear them from the synonymy: granulans var. rufipennis Hubenthal is identified as brevipalpis Bedel, and a lectotype designated; H. griseus var. lateralis Dalla Torre is left as incertae sedis and is classed as a nomen oblitum.