Two more species that would come to be included with "Edmontosaurus regalis" were named from Canadian remains in the 1920s, but both would initially be assigned to the genus "Thespesius". Gilmore named the first, "Thespesius edmontoni", in 1924. "T. edmontoni" also came from the Horseshoe Canyon Formation. It was based on NMC 8399, another nearly complete skeleton lacking most of the tail. NMC 8399 was discovered on the Red Deer River in 1912 by a Sternberg party. Its forelimbs, ossified tendons, and skin impressions were briefly described in 1913 and 1914 by Lambe, who at first thought it was an example of a species he'd named "Trachodon marginatus", but then changed his mind. The specimen became the first dinosaur skeleton to be mounted for exhibition in a Canadian museum. Gilmore found that his new species compared closely to what he called "Thespesius annectens", but left the two apart because of details of the arms and hands. He also noted that his species had more vertebrae than Marsh's in the back and neck, but proposed that Marsh was mistaken in assuming that the "annectens" specimens were complete in those regions.