We describe three new genera and four new species (three named) of siricomorph sawflies (Hymenoptera: Symphyta) from the Ypresian (early Eocene) Okanagan Highlands: Pamphiliidae, Ulteramus republicensis
new genus, new species from Republic, Washington, United States of America; Siricidae, Ypresiosirex orthosemos
new genus, new species from McAbee, British Columbia, Canada; and Cephidae, Cuspilongus cachecreekensis
new genus, new species from McAbee and another cephid treated as Cephinae species A from Horsefly River, British Columbia, Canada. These are the only currently established occurrences of any siricomorph family in the Ypresian. We treat the undescribed new siricoid from the Cretaceous Crato Formation of Brazil as belonging to the Pseudosiricidae, not Siricidae, and agree with various authors that the Ypresian Megapterites mirabilis Cockerell is an ant (Hymenoptera: Formicidae). The Miocene species Cephites oeningensis Heer and C. fragilis Heer, assigned to the Cephidae over a century and a half ago, are also ants. Many of the host plants that siricomporphs feed upon today first appeared in the Eocene, a number of these in the Okanagan Highlands in particular. The Okanagan Highlands sites where these wasps were found also had upper microthermal mean annual temperatures as are overwhelmingly preferred by most modern siricomorphs, but were uncommon in the globally warm Ypresian, only found then in higher elevations and highest latitudes.