NUMMULITES 



833 



up into a number of chamberlets having little or no direct communi- 

 cation with each other. 



Notwithstanding that the inner chambers are thus so deeply 

 buried in the mass of investing wholes, yet there is evidence that 



FIG. 632. Portion of a thin section of Nitinniiilitr.* l^-r/ijutu taken in the 

 direction of the preceding, highly magnified to show the minute structure 

 of the shell : ", a, portions of the ordinary shell-substance traversed by- 

 parallel tubuli ; b, b, portions forming the marginal cord, traversed by 

 diverging and larger tubnli ; c, one of the chambers laid open ; d, <1, il, 

 pillars of solid substance not perforated by tubuli. 



the segments of sarc;>de which they contained were not cut ofl' from 

 communication with the exterior, but that they may have retained 

 their vitality to the last . The shell itself is almost every- 

 where minutely porous, being penetrated by parallel tubuli, which 

 piiss directly from one surface to the other. These tubes are shown. 

 as divided lengthwise by a vertical section, in fig. 632, , a ; whilst 

 the appearance they present when cut across in a horizontal section 

 is shown in fig. 633, the 



- ! 



''"'I. 



transparent shell -substance 



a, , being closely dotted 



with minute punctations 



which mark their orifices. 



In that portion of the shell. 



however, which forms the 



margin of each whorl (fig. 



632, 6, b), the tubes are larger, 



and diverge from each other 



at greater intervals ; and it 



is shown by horizontal sections FIG. 633. Portion 



that they communicate tVcdv 



with each other laterally, so 



as to form a network such a.s 



seen at f>. h. fig. 634. At 



of horizontal section of 

 Nummulites showing the structure of the 

 walls and of the septa of the chambers : 

 , a, a, portion of the wall covering three 

 chambers, the punctations of which are the 

 orifices of tubuli ; b, b septa between these 

 chambers containing canals which send out 

 lateral branches, c, c, entering the chambers 

 by larger orifices, one of which is seen at (1. 



IS 



certain other points, d. d, d, 

 fig. 632, the shell -substance 

 is not perforated by tubes, but 

 is peculiarly dense in its texture, forming solid pillars which seem 

 to strengthen the other parts ; and in Nummulites whose surface.-, 

 have been much e.\|>< >>,<! to attrition, it commonly happens that the 

 pillars of the superficial layer, being harder than the ordinary shell- 

 substance, and bein- consequently less worn down, are left as 



3 H 



