On the Microscopic Structure of Nummulina, Orbitolites , and Orbitoides

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Abstract
A bout five years since, I was requested by my friend Mr. S. P. Pratt to endeavour to determine by microscopic examination the character of certain discoidal bodies, varying from about four to ten lines in diameter, which he had found in great abundance in the nummulitic deposits of Biaritz, and the nature of which could not be resolved by any ordinary means. Their circular form and limited dimensions seemed to indicate their relation either to the group of Nummulites or to that of Orbitolites . As they did not present any obvious trace of the chambered interior of the former tribe, they had been referred to the latter, notwithstanding the absence of visible pores on the surface and margins; and had been figured by M. Michelin, in his ‘Iconographie Palæontologique,’ under the designation of Orbitolites Prattii , and by M. D'Archiac as O. submedia . Applying to this fossil the same method of investigation with that which had been so successfully employed in the case of teeth, bones, and shells, I was soon able to bring to light its whole interior structure, which, in most specimens, is remarkably well preserved, in spite of its very unpromising external aspect. I found this structure entirely different, however, from anything with which I was at that time acquainted; and having brought it under the observation of many distinguished naturalists and palæontologists, among whom I may mention Professors Ehrenberg and Milne-Edwards, I found them equally unable to assign the place of this body in the animal series,

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