Excerpt from Some Eocene Diatoms From South Atlantic Cores: Part I. New and Rare Species of Arachnoidiscus; Part II. Rutilaria Greville Cells solitary, valves discoid, with a' circular, sub-circular or sub-triangular outline. Valve surface flat or nearly so, but often with the central por tion slightly raised or depressed. Valve surface divided into sectors by radiating costae (furrows or ribs). The primary costae proceed from the margin and almost reach the small circular and often hyaline central area. Between these are ...
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Excerpt from Some Eocene Diatoms From South Atlantic Cores: Part I. New and Rare Species of Arachnoidiscus; Part II. Rutilaria Greville Cells solitary, valves discoid, with a' circular, sub-circular or sub-triangular outline. Valve surface flat or nearly so, but often with the central por tion slightly raised or depressed. Valve surface divided into sectors by radiating costae (furrows or ribs). The primary costae proceed from the margin and almost reach the small circular and often hyaline central area. Between these are shorter secondary costae that usually penetrate the valve to a distance equal to about half the radius or less, while others, the tertiary costae, are usually much shorter and often restricted to the marginal zone as an elongated punctum. Valve surface of the inter-costal sectors areolate, areolae moderately large, usually sub-quadrate, sub-circular or sub-triangular, frequently more or less uniform in size though a little reduced asthey approach the valve margin. Areolae usually in continuous concentric circles, but in some species the lines of areolae on one sector alter nate with those on contiguous sectors. When the valve is intact, the areolae are furnished with dendritic outgrowths or volae that partially oc clude the aperture through the valve. In many fos sil species these structures are missing due to erosion. In some species a hexagonal system of ridges is superimposed upon the walls of the areolae, often these are eroded to provide an ir regluar pattern. Sometimes the walls of the areo lae are verrucose bearing small pustules at the intersection of the walls; in others fine costae or a series of reticulate lines are also arranged con centrically linking the primary radial costae and anastomosing over the valve surface giving it the appearance of a spider's web. Arachnoidiscus is usually found sessile on some of the smaller red algae that gather around the holdfasts of the larger kelps, and appears to favour the temperate and sub-tropical zones. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at ... 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.
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