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Hi Pentti,
definately not P. ventralis, which has an orange abdomen. I think it might be P. alpina with "disinct boreal distribution" and described from Finland and Swedish Lapland. Most important is the slightly elongated mid-frontal stripe in the female which is visible on the picture you gave after my first reply. In addition with missing hairs in upper posterior corner on anepisternum, slighly brownish cross-veins, size, coloration and distribution alpina fits well. Unfortunately I never have seen this species. I hope that you have collected this female. You should look out for more specimen.
Regards
Piet