Middle Tertiary marsupials (Mammalia) from North America

All species of North American marsupials from the Chadronian through Hemingfordian are reviewed. Most North American species of didelphids previously referred toPeratheriumare allocated toHerpetotherium.Five species ofHerpetotheriumare recognized. The ChadronianPeratherium donahoeiHough is synonymized withHerpetotherium valens(Lambe). The Orellan speciesHerpetotherium stevensoniCope is resurrected and referred, along with the ChadronianPeratherium titanelixMatthew, to a new genus,Copedelphys.BothCopedelphysandHerpetotheriumcan be derived from known Duchesnean species ofPeratheriumfrom North America. Two genera of peradectids are recognized,NanodelphysMcGrew andDidelphidectesHough.Nanodelphys minutusis synonymized with“Herpetotherium” huntiCope and a second species ofNanodelphysis recognized from the Arikareean, though not named.