"The species covered are Volucella arctica, bombylans (including forms bombylans, haemorrhoidalis and plumata), elegans, evecta, facialis, inanis, inflata, liquida, pellucens (ssp pelluscens), zonaria (ssp zonaria and beckeri), and there are comments on an undescribed species in North America." - Matthew Vosper
Identify observations on iNaturalist: https://www.inaturalist.org/observations/identify?place_id=97394%2C97391%2C97392&taxon_id=52481
With regard to couplet 5, females of the undescribed Pacific coast species have extensive yellow setae on the scutum and currently key out to V. facialis incorrectly. Only the males of the undescribed species have the black limited to the posterior scutum. See Volucellini Key for US/Canada.