Ulteramus republicensis is known only from one fossil, the part side of the holotype, specimen number UWBM 77532, which is housed in the collections of the Burke Museum of Natural History in Seattle, Washington.

The specimen is preserved as a compression fossil in silty yellow to grayish shale, which was recovered from outcrops of the Tom Thumb Tuff member of the Klondike Mountain Formation in 1993 by Wesley Wehr.

Ulteramus was first studied by the paleoentomologists S. Bruce Archibald from Simon Fraser University in Burnaby, British Columbia and Alexandr Rasnitsyn of the A.

The described fossil of Ulteramus is missing the majority of the wing apex area, but the small portion that is preserved seems to be smooth.

[1] U. republicensis was one of three sawfly species described in Archibald & Rasnitsyn's 2015 paper, the other two being Ypresiosirex orthosemos and Cuspilongus cachecreekensis, both from the McAbee fossil beds in south central British Columbia.