| Summary: | <span style="font-family: 'Times New Roman'; font-size: small;"><p>The <em>canaliculatus</em> species group of <em>Stenus</em> (<em>Nestus</em>) is redefined. Four new Palaearctic species of the group are described and illustrated: <em>S.</em> (<em>N.</em>) <em>alopex</em> sp. nov. from the Putorana Highland and Taymyr Peninsula, Russia; <em>S.</em> (<em>N.</em>) <em>canalis</em> sp. nov. from SE Siberia and the Russian Far East; <em>S.</em> (<em>N.</em>) <em>canosus</em> sp. nov. from the Narat Mt Ridge, Chinese Tien Shan; <em>S.</em> (<em>N.</em>) <em>delitor</em> 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. <em>S.</em> (<em>N.</em>) <em>milleporus</em> Casey, 1884 (= s<em>ectilifer</em> Casey, 1884) is revalidated as a species propria. <em>S.</em> (<em>N.</em>) <em>sphaerops</em> Casey, 1884 is redescribed; its aedeagus is figured for the first time; the aedeagus of <em>S.</em> (<em>N.</em>) <em>caseyi</em> 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 <em>S</em>. (<em>N</em>.) <em>melanopus</em> Marsham, 1802; its Siberian and NE European records are supposed to be erroneous; the monotypic <em>melanopus</em> species group is erected.</p><br /></span>
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