Excerpt from The Canadian Naturalist and Quarterly Journal of Science, Vol. 10: With the Proceedings of the Natural History Society of Montreal This genus was established by Salter, in 1858, for a very curious shell found in Scotland, in the Durness Limestone, one of the lowest members of the Lower Silurian or possibly within the limits of the Upper Cambrian. Salter found in this limestone two species of the genus, but one was too imperfect for description. The typical species P. invagination he regarded as the shell of a cephalopod mollusk allied to Orthoceras, but of very simple structure, having the chamber and siphuncle united into one organ. His definition of the genus was in these words; "siphuncle and septa combined, as a series of conical concave septa which fit into each other sheathwise." In 1860, Billings described, in the Canadian Naturalist, a species from the Calciferous Formation of Belleisle, under the name Piloceras Canadense. The specimens showed that the part described by Salter was not the external shell, but only the siphuncle, and that the shell, when complete, must have included a chambered portion surrounding this enormous siphuncle, which thus corresponded to the great siphuncle of the Lower Silurian shells known as Andoceras. 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.