832 



MICROSCOPIC FORMS OF ANIMAL LIFE 



edge being placed on a firm support ; or, if this method should not 

 succeed, by heating it in the flame of a spirit-lamp, and then throw- 

 ing it into cold water or striking it edgeways. ISTummxdites usually 

 show many more turns, and a more gradual rate of increase in the 

 breadth of the spire, than Foraminifera generally : this will be appa- 

 rent from an examination of the vertical section shown in fig. 631, 

 which is taken from one of the commonest and most characteristic 



B 



FIG. 630. A, piece of Niiuniuditic limestone from Pyrenees, 

 showing Nummulites laid open by fracture through median 

 plane ; B, Orbitoides. 



fossil examples of the genus, and which shows no fewer than ten convo- 

 lutions in a fragment that does not nearly extend to the centre of the 

 spire. This section also shows the complete inclosure of the older 

 convolutions by the newer, and the interposition of the alar prolonga- 

 tions of the chambers between the successive layers of the spiral 

 lamina. These prolongations are variously arranged in different 





FIG. 631. Vertical section of portion of Nintnnidites Icevigata : a, margin 

 6f external whorl ; b, one of the outer row of chambers ; c, c, whorl invested 

 by a ', (I, one of the chambers of the fourth whorl from the margin ; e, <', 

 marginal portions of the inclosed whorls ; /, investing portions of outer 

 whorl ; g, </, spaces left between the investing portion of successive whorl* ; 

 h, h, sections of the partitions dividing these. 



examples of the genus ; thus in some, as J'. distant, they keep their 

 own separate course, all tending radially towards the centre: in 

 others, as .T. /trr!</nt, their partitions inosculate with each other, so 

 as to divide the space intervening bet \veen each layer and the next 

 into an irregular network, presenting in vertical section the appear- 

 ance shown in fig. 6,'U ; whilst in .A', yarfinsciixis they are broken 



