Excerpt from A Monograph of West American Pyramidellid Mollusks In all the species of which the soft parts are known the external anatomy is very similar. In examining a large number of species, as noted by Fischer, intermediate types occur, until it becomes a matter of great difficulty to decide where, if anywhere, the generic lines can be drawn. It is not surprising that some authors have resorted to the expedient of regarding most of the species, notwithstanding the contrasted extremes of the series, as belonging to a single genus. When a group is composed of such a multitude of species, it seems more convenient in practice and leads more efficiently to clear thinking to take the other View, and subdivide the groups sufficiently to make it reasonably clear Where a given species belongs in the series. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.