558 DR. CARPENTER'S RESEARCHES ON THE FORAMINIFERA. 



102. The shelly plates which bound the chambered plane above and below, are 

 formed of a succession of superimposed lamellae (Plate XXXI. fig. 10). These lamellae, 

 which are of tolerably uniform thickness, are most numerous in the older or more cen- 

 tral portions of the disk, and diminish in number towards the marginal or last-formed 

 portions ; so that it seems pretty certain that new lamellae must be added from time 

 to time, as the disk is augmented by the formation of new annuli. I have often met 

 with appearances, which might seem to indicate that the formation of a new lamella 

 over the entire surface of the disk, and the addition of a new annulus at its margin, 

 were parts of one and the same act of growth, the new lamella being continued into 

 the annular septum ; but if this were constantly the case, the number of lamellae 

 which form the ceiling or floor of any chamber, would always correspond with the 

 number of annuli external to it, which I do not find to hold-good. 



103. Each of these lamellae is perforated by an assemblage of parallel tubuli very 

 closely set-together, which pass from its inner towards its outer surface (Plate XXXI. 

 figs. 9, 10) ; and there is such a continuity between the tubuli of successive lamellae, 

 that a communication is thus established between the cavity of the thickest-walled 

 chamber, and the external surface of the disk. These tubuli, however, are very mi- 

 nute, their diameter being not above i ,ooo tn of an inch. They are wanting in cer- 

 tain parts of the shell, which then presents a transparence that contrasts strikingly 

 with the semi-opacity produced by the tubular perforations. By the comparison of 

 vertical with horizontal sections taken in different planes, it appears that these trans- 

 parent portions of the shell have a conical form, the base of each being on the sur- 

 face of the shell, and its apex pointing to one of the angles at the outer margin of a 

 chamber (Plate XXX. fig. 4, cc, dd). Their gradual widening towards the surface 

 causes the diameter of their bases to increase with every addition to the thickness of 

 the shell ; and thus it is on the older portion of the shell, and especially on its cen- 

 tral protuberance, that they become most conspicuous as rounded ' punctations' 

 ( 96). In horizontal sections of the superficial lamellaa, they form a large proportion 

 of the area (Plate XXXI. fig. 6); whilst in similar sections near the chambered plane 

 (fig. 9), they become blended with angular projections of the annular partitions, that 

 fill-up the spaces left between the proper walls of the chambers by the rounding-off 

 of their angles. 



104. The lamellated structure is seen in these conical pillars (Plate XXXI. fig. 

 10, b), the lamellae being continuous with those of the tubular part of the shell; so 

 that at each increase in thickness, a tubular and a non-tubular portion must be super- 

 imposed upon the corresponding parts of the preceding lamella. Both in the tubular 

 structure of the shell, and in the presence of these non-tubular columns, there is an 

 exact conformity to the structure of Nummulite and its congeners*. 



* I avail myself of this opportunity of correcting a mistake into which I fell in my original description 

 of the structure of Nummulite (Quart. Journ. of Geol. Soc., 1850, p. 26), in regarding the non-tubular 

 columns of the shell as having been passages which had become filled-up by the infiltration of carbonate of lime 



