MSSIL CORALS. 



65 



Tabiclata, which would at once make It clear why the 

 tabulate corals appear in such numbers of species and 

 individuals in the Silurian and Devonian seas. In the 

 Carboniferous rocks the most numerous corals are the 

 rugose kind, in which the radiated structure is very 

 plainly visible, as in Lithostrotion junceum, etc., of 

 which we give illustrations of the transverse appear- 

 ance they present when cut and polished. For some 

 of my illustrations I am indebted to Mr. James 

 Thomson, F.G.S., of Glasgow — one of the most 



Fig. 47. — Horizontal section of ^/////t'.vw^ 

 coralloidcs, showing feebly developed septa. 



Fig. 48. — Cyathaxitiia (Carboniferous 

 limestone). A, horizontal section. 



enthusiastic and diligent students of Palaeozoic fossil 

 corals in Europe. I have already said that the 

 numerously represented fossils called Stromatopora — 

 abundant in our Silurian and Devonian limestones — 

 are now believed to be calcareous sponges, or sponges 

 whose abundant limy spicules amalgamated into the 

 concentric rings characteristic of their structure. This 

 structure may be studied in any polished mantelpiece 

 formed of Devonian marble from the quarries of 

 Newton Abbot and the neighbourhood. By far the 

 prettiest of the Palaeozoic fossil corals are those 



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