EXPLANATION OP PLATE XVII. 



Halysites australis, Eth. fil. 



Fig. 1. Portion of a corallum, seen from above, showing the form of the 

 reticulating laminae, and the normal corallites. 



,, 2. Small portion of the same with the normal corallites and the 

 interstitial tubes. Enlarged. 



,, 3. Portion of another corallum differing from that seen in fig. 1 only 

 in the size of the reticulating lamina;. 



,, 4. The sj,me. Enlarged. 



„ 5. Portion of another corallum seen obliquely from the side, showing 

 the lateral faces of the laminae, and outline of the normal 

 corallites. 



,, G. Horizontal section of part of a lamina, with two normal corallites 

 and two interstitial tubes filled with crystalline calcite. 

 Parts of the lamina walls are converted into chalcedony, 

 particularly on the upper right hand ; two blebs are also 

 visible on the opposite side. X 18 (about). 



„ 7 Vertical section showing two normal corallites with close hori- 

 zontal tabula3, between them an interstitial tube with 

 distant tabulae. The intertabular, or visceral cavities of 

 the normal corallites are filled with crystalline calcite ; the 

 interstitial tube on the extreme right has been converted 

 into a mass of chalcedony, the walls and tabulae of that in 

 the centre are in the same condition, whilst scattered on 

 the left hand are blebs of chalcedony. X 20 (about). 



,, 8. Vertical section of a normal corallite, highly altered. The 

 tabulae and portions of the walls remain as sclerenchyma, 

 the other parts of the latter being converted into blebs of 

 chalcedony. The intertabular, or visceral spaces, are filled 

 with crystalline calcite. X 20 (about). 



