STRUCTURE OF NUMMULITES. 



511 



in the breadth, of the Spire, than Foraminifera generally; this will 

 he apparent from an examination of the Vertical section shown in 

 Fig. 257, which is taken from one of the commonest and most 

 characteristic Fossil examples of the genus, and which shows no 

 fewer than ten convolutions in a fragment that does not by any 

 means extend to the centre of the spire. This section also shows 

 the complete enclosure of the older convolutions by the newer, 

 and the interposition of the Alar prolongations of the Chambers 

 between the successive layers of the Spiral lamina. These pro- 

 longations are variously arranged in different examples of the 

 genus ; thus in some, as N. distans, they keep their own separate 

 course, all tending radially towards the centre ; in others, as 

 N. laevigata, their partitions inosculate with each other, so as to 

 divide the space intervening between each layer and the next into 

 an irregular network, presenting in vertical section the appearance 

 shown in Fig. 257 ; whilst in JV. garansensis they are broken 



Fig. 257 



Vertical Section of portion of Nummulina Icevigata : —a, margin 

 of external Whorl ; b, one of the outer row of Chambers ; c, c, 

 Whorl invested by a ; d, one of the Chambers of the fourth Whorl 

 from the margin ; e, e, marginal portions of the enclosed Whorls ; 

 /", investing portion of outer Whorl ; g, g, spaces left between 

 the investing poilions of successive Whorls; h, h, sections of the 

 Partitions dividing these. 



up into a number of Chamberlets, having little or no direct com- 

 munication with each other. 



393. Notwithstanding that the inner chambers are thus so 

 deeply buried in the mass of investing whorls, yet there is evidence 

 that the segments of Sarcode which they contained were not cut 

 off from communication with the exterior, but that they may have 

 retained their vitality to the last. The Shell itself is almost 

 everywhere minutely porous, being penetrated by parallel Tubuli 

 which pass directly from one surface to the other. These tubes 

 are shown, as divided lengthways by a Vertical section, in Fig. 258, 



