Excerpt from The Genera of Recent Mollusca, Vol. 2 of 3: Arranged According to Their Organization Gills exposed, or only slightly covered by a fold of the mantle, situated behind the heart, and never lodged in a distinct, cervical cavity. Sexes united in the same indi vidual. Abdomen rudimentary, not spirally developed in the adult, or protected by a shell. Larva shell-bearing, and furnished with deciduous cephalic fins. 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.