Excerpt from Bulletins of American Paleontology, 1943, Vol. 28 The last two types of calcite represent the geodic filling of cavi ties in the shell; here, as is usual in such cases, crystallization be gins with numerous fine small crystals around the periphery of the cavity and ends with the deposition of coarse and rather ir regular crystals at the center. However, the thin white lines re main to be explained, and must represent the position of some substance which controlled the pattern of calcite deposition. The course of these lines is shown in text figure 1, though no attempt has been made to differentiate the two types of calcite which to gether make up the geodic filling. It is apparent from the con dition of the specimen that the white lines must represent a struc ture which was present before calcite was deposited in the camerae. Further, the form of the line suggests that it was a thin tissue, which, if stretched out, would approximately line the camerae. The conclusion seems unavoidable that this represents a portion of the original cameral tissue which has become separated in part from the septa, to which it was originally attached, and was lying in a somewhat dis-torted condition in the camerae. 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.