22 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 2, 



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 sur- 

 face and margins ; and had been figured by M. Michelin, in his 

 * Iconographie Paleeontologique,' under the designation of Orbitolites 

 Pimttii, 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 struc- 

 ture, which, in most specimens, is remarkably well preserved, in spite 

 of its very unpromising external aspect. I found this structure en- 

 tirely different, however, from anything with which I was at that 

 time acquainted ; and having brought it under the observation of 

 many distinguished naturalists and palaeontologists, 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, some of them even inclining to the opinion that its nature is 

 vegetable. With the view of throwing light upon this question, I 

 entered upon a more careful examination than had been previously 

 made, into the minute structure of Nummulifes and Orbitolites ; and 

 as many of the results which I have thus obtained appear to me to 

 be both novel and interesting, I trust that an account «f them may 

 not be unacceptable to the Geological Society. In the course of these 

 inquiries, I have been led to include the new genus Orbitoides, esta- 

 blished by M. D'Orbigny for the reception of the so-called Nummu- 

 lites Mantelli and allied species* ; and it will be seen that my results 

 fully confirm the propriety of the institution of this genus, for which 

 they afford very positive characters ; whilst they bring into it Mr. 

 Pratt's problematical fossil, together with several others which had 

 been previously considered as Nummulites. 



NUMMULINA. 



My inquiries into the minute structure of Nummulites have been 

 principally carried on upon the Nummulina Icevigata (Lamarck) of 

 the London clay formation; both as being the species most easily 

 procured, and also as being generally in a condition remarkably well 

 adapted for minute examination. The Nummulites from a calcareous 

 matrix have generally undergone a considerable change in the pro- 

 cess of fossilization ; their chambers and passages being entirely filled 

 up by calcareous infiltration, and the texture of the shell itself being 

 usually so altered, as to give very little indication of its original cha- 

 racter, in a large proportion of the Nummulites from Bracklesham 

 Bay, on the other hand, the clayey nature of the matrix has preserved 

 the shells almost unchanged, and the chambers are usually free from 

 infiltration. Such specimens are obviously the best adapted, there- 

 fore, to afford indications of the original characters of the shell, and 

 also of the animal, or assemblage of animals, to which it served as a 

 protection. 



* Quarterly Journal of the Geological Society, vol. iv. p. 12. 



