A new specimen of Struthiomimus altus is described from the Oldman Formation of Alberta. Ossified xiphisternal structures are present, which are similar to the posterolateral processes of the sternum of some birds. The gastralia are found to consist of two, rather than three, overlapping segments.Four genera of Upper Cretaceous ornithomimids are recognized: Struthiomimus, Ornithomimus, Dromiceiomimus, and Gallimimus. The structure of the manus is found to be the most reliable character suite distinguishing them. Dromiceiomimus, however, can still be distinguished only on the basis of limb proportions, and its recognition remains tentative until further material is forthcoming.