1849.] CARPENTER ON THE STRUCTURE OF ORBITOIDES. 35 



to cut through in examining a piece of nummuhtic hmestone. This 

 might be readily mistaken for a NummuUte, upon a cursory examina- 

 tion ; but that it does not belong to that group is obvious from the 

 want of numerical correspondence between the number of investing 

 layers and that of the chambers in the central plane, as well as by 

 the want of continuity in the investing layers themselves. And a 

 careful comparison of it with the corresponding section of Orhitoides 

 Prattii (fig. 3.5) will show that it differs from that species in no other 

 important particular, than in the larger relative size and smaller 

 number of the chambers in the central plane. 



Among the specimens obtained by Capt. Grant and Capt. Vickary 

 from the nummulitic limestone of North- Western India, and hitherto 

 regarded as Nummulites, I have obtained one, as already stated, 

 which I believe to be identical with the Orhitoides Mantelli of North 

 America. But besides this, I have met with four or five other species, 

 which seem to be clearly referable to the same generic type, although 

 differing in certain important particulars. A vertical section of one 

 of these, taken from a species hitherto, I believe, undescribed, is 

 shown in fig. 1 9 ; and it is there seen that the central layer of cells 

 bears an extremely small proportion to the entire thickness of the 

 specimen (the edge of which is broken away at its lower part), and 

 that the investing layers present the appearance of being traversed 

 by conical passages, extending from each surface towards the central 

 layer. These passages, being filled up with the opake matter of the 

 matrix, look darker than the surrounding structure of the fossil. The 

 appearance presented by a vertical section of the Lycophris dispansus 

 of Sowerby is very nearly the same ; and the surface of this body 

 exhibits large punctations, which obviously mark the entrances to 

 these passages. The structure of Lycophris ephippium is the same ; 

 and it is worthy of notice that its peculiarities had been perceived and 

 delineated by Mr. Sowerby (Geol. Trans. 2nd Ser. vol. v. pi. 24. 

 fig. 15), who describes as pillars what are in my apprehension nothing 

 more than the columns of opake matter filling the perforations. In 

 fig. 13 is represented a vertical section, and in fig. 14 a horizontal 

 section passing through the central plane, of an undescribed fossil 

 from Scinde, which obviously belongs to the same genus, although 

 presenting the external aspect of a Nummulite. Its diameter was 

 about an inch, and its thickness about one-fifth of an inch. Here, 

 too, we observe the central layer (a, a) to be extremely thin in com- 

 parison with the layers (b, b) by which it is invested on either side ; 

 and these do not thin away towards the edge, as we see them to do 

 in most other species, but the outer portion of them is prolonged 

 from both surfaces over the margin of the disk, so as to meet (as at c) 

 and completely inclose the central layer, — a peculiarity which I have 

 nowhere else seen. I think it not improbable that this may be the 

 adult condition of some of the smaller species. The superficial layers 

 are evidently traversed, as in the preceding cases, by passages now 

 filled with opake matter (d, d). The chambered layer, as seen in 

 the horizontal section (fig. 14, a, a), closely corresponds with that of 

 Orbitoides Prattii (fig. 32) ; but the investing layer is distinguished 



d2 



