Excerpt from Conchologia Iconica, or Illustrations of the Shells of Molluscous Animals, Vol. 13: Containing Monographs of the Genera Terebratula, Lingula, Vitrina, Rynchonella, Cymbium, Simpulopsis, Crania, Cyclostoma, Phasianella, Orbicula, Cyclophorus, Trochus, Leptopoma The Terebratula; live at various depths, reaching nearly to the deepest limit of molluscan life, attached to corals, stones, fragments of shells, and to one another. The na tural position of the animal is to repose upon its back, the smaller or dorsal valve being undermost, and a mooring is secured by means of the byssus-like tendon or pedicle let down from the overhanging ventral valve, which is beaked on one side and perforated for the purpose. The perforation is very liable to erosion and damage from the buffeting of the water, more so in some species than in others, and it becomes more or less enlarged accordingly. To meet this the area below the perforation is constructed of a pair of plates, termed the deltidium, and as the foramen enlarges, the plates separate from each other like a sliding panel. The substance of the shell is invariably punctured throughout, differing generically in this respect from that of Rbgncbonclla, and it is a beautiful Object under the microscopic, or even under an ordinary lens. 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.