278 Professors King and Rowney's 



layers, the chambers, and the walls, vertical and oblique sec- 

 tions of a nummulite are rarely without some apparent devia- 

 tions from the general plan of structural arrangement. 



We have represented in figures 1 and 2 (PL XIX.), as faith- 

 fully as our abilities will allow, two medio-vertical sections, 

 displaying the forementioned characters. Fig. 1, a section of 

 Nummulites Icevigatus^ns, seen magnified 120 diameters, shows 

 a portion of two layers, between which is a series of investing 

 chambers (a), and underneath other three that are median 

 (a x). The walls (c), including their extensions (c x), pass 

 through the layers with a slight curve : it is noteworthy tliat 

 one of them ends at the floor of an overlying chamber. The 

 only structures discernible in these parts are a few transverse 

 lines, which characterize the entire layers, and evidently 

 belong to their constituent laminae. The chamber-roofs (b) 

 are distinctly tubulated, as represented by the black lines : the 

 tubules run straight out for the most part, but with a slight 

 curve occasionally *. Fig. 2 represents a section of Num- 

 mulites broachensis (attached, with five more, to the slide pre- 

 sented to us by Mr. H. J. Carter) — a tumid species, with its 

 different parts less repetitively develoj^ed than in many others. 

 The chamber-roofs {b) have the tubules (marked in the figure 

 by dark lines) filled with yellow ('? hydrous) oxide of ironf; 

 causing them to appear strongly in contrast to the white semi- 

 opaque walls (c, c x) : the latter parts everywhere display a 

 fine asbestine structure. Every layer, besides being tubular 

 and asbestine, is distinctly laminated, the laminae traversing 



traces of tubulatiou, while otliers in immediate connexion are perfectly- 

 pellucid and structureless. We have never seen asbestine structure in 

 Nummulites la-vif/atus ; but in another species, fx'oni Biarritz, the walls ex- 

 hibit a vertical lineation, though indefinitely, which appears to be due to 

 it. Whether the structure be original, or superinduced does not affect 

 the question ; for the parts characterized by it, if they were even struc- 

 tureless, would be different from the roofs. Mr. H. J. Carter has deli- 

 neated the walls and their extensions (" columns of condensed 8hell-sul> 

 stance ") of Orbitoides dispansa, with something like a prismatic structure 

 (Ann. Nat. Hist. 3 ser. vol. viii. pi. xvi. fig. 1 d), which maybe asbestine ; 

 or, possibly, from being fasciculated and divergent, it is due to the canal- 

 system : if the former, the case is the only one known to us, with the 

 exception of the doubtful one represented by D'Archiac and Haime, of 

 the asbestine structure having been published. Mr. Carter, however, has 

 been for some time acquainted with it in Nummulites broachensis : and it 

 was from him we first got our information on the matter. 



* The roof and wall belonging to the median chamber on the left side 

 are broken : they lie below the plane of the section, and therefore come 

 out indefinitely. 



t The chambers, also the canals, are filled with a red variety, which 

 may be anhydrous oxide of iron. 



