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 to Peratherium are allocated to Herpetotherium. Five species of Herpetotherium are recognized. The Chadronian Peratherium donahoei Hough is synonymized with Herpetotherium valens (Lambe). The Orellan species Herpetotherium stevensoni Cope is resurrected and referred, along with the Chadronian Peratherium titanelix Matthew, to a new genus, Copedelphys. Both Copedelphys and Herpetotherium can be derived from known Duchesnean species of Peratherium from North America. Two genera of peradectids are recognized, Nanodelphys McGrew and Didelphidectes Hough. Nanodelphys minutus is synonymized with ''Herpetotherium'' hunti Cope and a second species of Nanodelphys is recognized from the Arikareean, though not named.