New species and records of Stenus (Nestus) of the canaliculatus group, with the erection of a new species group (Insecta: Coleoptera: Staphylinidae: Steninae)

The canaliculatus species group of Stenus (Nestus) is redefined. Four new Palaearctic species of the group are described and illustrated: S. (N.) alopex sp. nov. from the Putorana Highland and Taymyr Peninsula, Russia; S. (N.) canalis sp. nov. from SE Siberia and the Russian Far East; S. (N.) canosus sp. nov. from the Narat Mt Ridge, Chinese Tien Shan; S. (N.) delitor sp. nov. from C & SE Siberia. New distributional data as well as brief analyses of old records for fourteen species described earlier are provided from both Palaearctic and Nearctic material. S. (N.) milleporus Casey, 1884 ​(= sectilifer Casey, 1884) is revalidated as a species propria. S. (N.) sphaerops Casey, 1884 is redescribed; its aedeagus is figured for the first time; the aedeagus of S. (N.) caseyi Puthz, 1972 as well as aedeagi of eight previously described Palaearctic species are illustrated anew. A key for the identification of all the known Palaearctic species of the group is given. A morphology and ecology based analysis of the main evolutionary trends within the group is provided. A lectotype is designated for S. (N.) melanopus Marsham, 1802; its Siberian and NE European records are supposed to be erroneous; the monotypic melanopus species group is erected.