MADREPORARIAN CORALS 65 



The upper surface of a Fungia of this type is slightly 

 convex and frequently raised into a shallow mound towards 

 the centre. The under surface is slightly concave, so that 

 the coral rests on its margin when placed on a liat table. 

 The upper surface is provided with a very large number of 

 vertical radially disposed laminae — the septa — with sharp 

 dentate or sinuous edges. The under surface is marked by 

 a corresponding series of shallow radial ridges — the costae — 

 armed with rows of blunt tubercles. Between the ridges on 

 the under side there is solid coral substance representing 

 the theca of the cup corals. In the centre of the under 

 surface there may be an ill-defined circular area, better 

 recognised in small than in large specimens, somewhat raised 

 or depressed and free from costal ridges. This will be 

 referred to as the " scar." 



In the centre of the upper surface there is a deep groove 

 or fossa from which the septa radiate to the margin of the 

 coral. This fossa may be taken as an indication that the 

 coral does not exhibit perfect radial symmetry but may be 

 divided into two laterally symmetrical halves along a 

 diameter, which may be called the directive diameter and 

 is parallel with the median line of the fossa. 



The septa are so numerous and close set that there is 

 difficulty in counting them and reducing them to a system ; 

 but in a good specimen a large septum can be seen passing 

 from each end of the fossa to the periphery in the same 

 plane as the directive diameter. These are the directive 

 septa. And on each side of the plane there are five other 

 large septa which pass from the side of the fossa to the 

 margin. 



These ten septa together with the two directive septa 

 constitute the primary twelve septa of the coral and were 

 the earliest septa to be formed in the development of the 

 coral. The other septa have been formed later and inter- 

 posed between the primaries in series, and thus we have 

 secondaries, tertiaries, and quaternaries, etc., each series of 

 septa being smaller than the preceding series and approaching 

 less closely to the fossa. The determination of the series 

 of septa in any specimen of good size requires the exercise 



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