The present volume contains the results of researches on the Post-Oligocene fossil bryozoa of North America and forms the concluding part of our studies on the Tertiary and Quaternary faunas, those of the Eocene and Oligocene epochs having been published in 1920 under the title of North American Early Tertiary Bryozoa. The present work, like the companion volume on Early Tertiary faunas, was undertaken under the joint auspices of the United States Geological Survey and United States National Museum. Almost without exceptiion all the type specimens described and illustrated in the present volume are contained in the paleontological collections of the United States National Museum.