6 



Prof. H. A. Nicholson on the Structure and 



in certain recent species of Allopora. In the phosphatized 

 specimens of Parkeria the original granules of carbonate of 

 lime have been replaced by granules of phosphate of lime ; 

 and if the specimen is non-infiltrated, i. e. has its chambers 

 empty, the skeleton-fibre then assumes a peculiar " sandy " 

 aspect. 1 have, however, failed to find in decalcified sections 

 of any of the specimens which I have examined any sand- 

 grains properly so-called ; and I am therefore led to conclude 

 that they did not exist, since it cannot be supposed that 

 grains of quartz should have been replaced during fossilization 

 by grains of phosphate or carbonate of lime. 



'6. Minute Structure of the Skeleton. 



The skeleton of Parkeria consists of radiating columns 

 (" radial pillars "), united by concentrically disposed lamell*, 



Vertical section across the centre of a specimen of rarkeria, enlars 

 twice. 2^f one of the radial pillars ; c, one of the chamberlets." 



