30 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 2, 



even genera of corals have been founded upon variations in the mode 

 of growth in one and the same species ; and I am disposed to beheve 

 that the range of variation is almost equally great in some species of 

 Nummulites. I have carefully examined many individuals differing 

 widely in external form, without being able to detect in them any 

 difference in internal structure at all worthy of being accounted a 

 specific character ; and this will not be deemed surprising after what 

 I have already stated, respecting the irregularities which may occur 

 in the consecutive chambers of a single whorl. Differences in the 

 proportion between the diameter and thickness of the disk, appear 

 to me to be especially unsatisfactory as specific characters ; for I 

 have met with specimens almost lenticular, which could not be dis- 

 criminated by any other indications from specimens of a nearly glo- 

 bular form. It is obvious that such differences may arise from 

 variations in the thickness of the calcareous deposit ; such as are 

 continually seen in the polypidoms of Zoophytes, and in the shells of 

 Mollusca. 



Without at present entering in detail upon the question of specific 

 distinctions, I may mention that the genus Nummulina appears to 

 me to be divisible in the first instance into two subgenera ; of which 

 one shall comprise the species in which the investing whorls are in 

 close apposition with each other, except at their margins, so that 

 the chambers of each whorl surround the preceding, without covering 

 them ; whilst in the other, the new chambers are prolonged over those 

 of the preceding whorl, so that the investing whorls of the shell are 

 only connected with each other by the prolongations of the inter- 

 cameral partitions. 



For the further subdivision of these groups, I am disposed to be- 

 lieve that the modes of arrangement of the prolongations of the septa 

 between the contiguous surfaces of the investing whorls, will prove 

 to be a character of great value in addition to those on which reliance 

 is at present placed ; as will, also, the disposition of the perforations 

 which I suppose to give exit to the pseudopodia. I may remark, 

 that the genus Lycophris, created by Montfort for the reception of 

 certain species in which the superficial punctations caused by these 

 perforations are especially noticeable, cannot be any longer maintainedj 

 since my examinations prove, not merely that these perforations are 

 common to Nummulites in general, but that the so-called Lycophris 

 scabi'osus of Sowerby is nothing else than an ordinary Nummulite, 

 whilst the Lycophris dispansus and Jjycophris ephippium of Sowerby 

 do not belong to this group at all, but are indubitable Orbitoides. 



Orbitolites. 



There can be no doubt, that, under this designation, various objects 

 have been assembled which have no real relationship to each other. 

 My observations have been made upon Orbitolites complanata of the 

 Paris basin, and upon a recent species from the Australian seas, very 

 closely allied to it, which is referred to by Prof. E. Forbes (Quarterly 

 Journal of the Geological Society, vol. iv. p. 12) as having been 

 apparently known to Defrance, and as probably the Marginopora of 



