Publisher's Synopsis
Excerpt from Philosophical Transactions, Vol. 3: Researches on the Foraminifera
145. Another marked feature of difference among the specimens of this Collection, is the depression or elevation of the central region relatively to the peripheral. In what I have assumed as the typical form, the central region presents the same general level with the rest, though the umbilicus itself is often marked by a prominent tubercle. In such forms as are represented in Plate 111. Figs. 1 and 2, the umbilical region is rather depressed than elevated; and this depression is often observed in older specimens whose early growth has taken place on.this type. But there is a group of specimens, of which three successive ages are represented in Plate III. Figs. 3, 4, 5, 8, that have the whole central region so exceedingly prominent as to form a cone, -whose apex is marked either by one large tubercle, or by a cluster of smaller ones; and this conformation gives so peculiar a physiognomy to the shells which present it, that few systematists would hesi tate in placing them apart as specifically different from the rest. On a careful compari son of a large number of individuals, however, it becomes apparent that this difference, like the preceding, is gradational; every degree of prominence being traceable from the individuals which have the umbilicus marked only by a tubercle, as in fig. 7, through those In which the region generally is slightly elevated, as in fig. 8, to those 111 which it presents the most marked projection, as in figs. 3 5. We shall presently find (fl' 153) that this difference depends mainly on the degree in which the investing layer, prolonged from the later convolutions over the surface of the earlier, is separated from that surface by the extension of the alar prolongations of the chambers of the investing whorls; as to which point there is a most remarkable diversity, not only among different individuals, but between the several convolutions of the same individual. 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.
