302 FAMILY NUMMULINIDA. 



• Nummuliles, by the changes in the texture of the shell which have taken place in fos- 

 silization. 



506. In both forms of Orbitoides, and not (as stated by Mr. Carter) in 0. Fortisii only, 

 we often find the superficial layers traversed by columns of non-tubular substance, which are 

 of conical form, having their bases on the two surfaces (where they commonly form prominent 

 tubercles), whilst their apices rest on the vertical partitions of the chambers of the median layer 

 (fig. 2, e, e). These columns are most developed in the large, thick 0. Fortisii of Scinde, in 

 which they are both large and numerous (figs. 10, 11) ; and being usually rendered opake by 

 pecuhar changes in fossilization, they present the appearance, in sections parallel to the 

 median plane, of opaque spots, e, e, figs. 12, 13, the diameter of which in proportion 

 to that of the chamberlets varies according to the depth at which the section has passed, 

 being of course greater as its plane is nearer to the surface. In the small, thin varieties of 

 this fossil which present themselves abundantly in Southern Europe, the columns are 

 frequently wanting altogether, and if present are very insignificant in size. In the American 

 variety of 0. Mantelli I have not met with any indication of the presence of these columns ; 

 but they are very conspicuous in some of the Scindian specimens of that type, although 

 entirely absent in others, — this variation in their development being in harmony M'ith the 

 similar variation that occurs among Nummulites. The columns, when present, always occur 

 at the points of junction of three or more of the partitions between the chamberlets, as is 

 shown in figs. 2, 12, 13, 14, and may be regarded as formed by an augmented development 

 of shell-substance at those points, as shown at e, c, fig. 16. When they are brought into 

 view by vertical sections of thick specimens, it very often happens that they are only 

 traversed by the plane of section for a part of their length, as shown in figs. 10, 15 ; but it 

 must not be supposed that they really stop short, as they seem to do, since there can be no 

 reasonable doubt of their continuity through the successive laminoe of the superficial layer, 

 as shown in the lower part of fig. 10. 



507. The indications of a canal-system which I have met with in 0. Fortisii have been 

 sufficient, when interpreted by the distribution of that system in Ci/docypeus, to justify the 

 belief that it is essentially the same in the former case as in the latter. I have been able 

 clearly to make out annular canals intervening between the successive rings of chamberlets, 

 and cross branches connecting these which run between the two lamella; of the partitions 

 between the chamberlets, as shown in fig. 3; and I can also perceive indications (as in 

 figs. 10, II), that the conical columns were traversed by branches of the same system, which 

 pass in them towards the surface. Even in the partitions between the superficial chamberlets 

 I have been able to detect traces of canals (shown in the upper part of fig. 9), just as in the 

 partitions that subdivide the alar prolongations of the chambers of the reticulate Nummulites. 

 The interseptal canal-system of the median plane is nearly as well displayed in the " cast" 

 represented in Plate XXII, fig. 5, as it is in my ideal figure of that system in Ci/cloc/i/pei/s 

 (which was drawn without the least knowledge of Prof. Ehrenberg's casts) ; so that if the 

 former really represents an Orbitoides, which there is no reason to question, the entire con- 

 formity in structure between the median chambered planes of these two organisms is extra- 

 ordinarily close. — I have not succeeded in making out the canal-system of 0. Mantelli with 



