A Revision of the Orbitoides of Christmas Island, (Indian Ocean)

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Abstract
In Andrews's monograph on Christmas, Island, published in 1900 (11), Prof. T. Rupert Jones & Mr. F. Chapman contributed an article on the Tertiary foraminiferal limestones, and described several new species of Orbitoides. It was my original intention to examine the Orbitoides, in order to ascertain whether with their aid new light could be thrown on the age of the deposits, as at the time when they were described the genus Lepidocyclina was little known. In doing so I found that the above-mentioned authors, in describing the species, omitted details which of recent years have become of prime importance in the recognition of these forms. Since their descriptions are frequently inadequate, considerable confusion about the Christmas Island Orbitoides has appeared in the literature. I have, therefore, been led to attempt a revision of Jones's & Chapman's species. I have been fortunately able to prepare numerous new microscopic slides from rock-material preserved in the British Museum (Natural History). and also have examined the slides containing Jones's & Chapman's figured types. Dr. W. D. Lang and Mr. W. Campbell Smith have kindly helped by arranging to have numerous sections cut in the Geological and Mineralogical Departments of the Museum. In all, about a hundred slides have been examined. In studying the Orbitoides the chief difficulty is that they are irregularly distributed in massive limestone, so that it necessitates much care to cut a section through a specimen in a particular desired direction. In no case are specimens weathered out so as to

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