As foreshadowed in the Preface to Part V of this memoir, the present contribution completes the work begun in 1885. It contains the remainder of the Pelecypoda and the Brachiopoda, together with a general summary of the geological and paleontological results and a few additions and corrections to earlier parts. As the student of these volumes will have observed (as is inevitable in such an undertaking, extending over 18 years of labor in the field and in the laboratory), there are some modifications of the original method, some shifting of the point of view with greater knowledge of the facts, and the introduction of some improvements due to increased experience. Black and white plates.