214 CEYLON PEARL OYSTER REPORT. 



The C o r al 1 u m. Tn the majority of specimens there are forty-eight septa, which, 

 according to Milne-Edwards and Haime'k system of notation, would be described as 

 being regularly arranged in six systems and four cycles. It will become obvious, 

 however, that the septa have been developed according to Duerden's and Pourtales' 

 law, and that what are apparently the quaternary septa are really exoccelic septa 

 belonging to the second cycle in order of appearance. In some few specimens the 

 normal regularity of the septal arrangement is disturbed by the development of one 

 or two additional septa in one or more of the systems. These additional septa are 

 always inserted between the apparent tertiaries and the apparent quaternaries 

 adjacent to them, and suggest the commencement of a fifth septal cycle, but in every 

 system in which they occur there is so much irregularity in the septal arrangement 

 that I attribute their presence to a process of re-growth and repair rather than to the 

 formation of a new cvcle. The normal arrangement of the septa is shown in fig. IT. 

 There are three cycles of endosepta. The six primaries are prominently exsert and 

 their inner ends bear large paliform lobes just before they unite with the columella. 

 The secondary endosepta are likewise prominent and exsert, and there are two or 

 three prominent vertical pali at the inner extremity of each. The innermost of these 

 pali can with difficulty be distinguished from the vertical upgrowths of the columella, 

 and the outermost is fused to the inner free margin of the septum, so that there is a 

 transition between " true pali" and " paliform lobes." I am inclined to think that the 

 sharp distinction drawn between these paliform structures is artificial and untenable. 

 The inner ends of the third cycle of endosepta converge towards the secondaries and 

 unite with them just outside the columella through the intervention of palial 

 upgrowths. In specimens that have been rubbed down, the pali in front of the 

 secondary and tertiary septa are seen to unite to form a chevron, similar to the 

 chevrons characteristic of Deltocyathus. 



Between every two endosepta there is an exoseptum. and in the deeper parts of the 

 corallum, i.e., below the level of the exsert portions of the septa, these exosepta are 

 seen to be united to the adjacent endosepta by tangential bars which, although they 

 do not exactly correspond to the similarly named structures of the Fungiidee, must be 

 described as synapticula. Their arrangement is very regular and characteristic. 

 Each primary endoseptum is joined to the exoseptum on either side of it by a 

 synapticulum which curves downwards and inwards to the fossa. These primary 

 synapticula, as they may be called, are equidistant from the centre of the coral, and 

 are situated nearer the centre than the others, so they form a sort of inner 

 synapticular ring. Each secondary endoseptum is similarly joined to the two adjacent 

 exosepta by synapticula which are situated somewhat further from the centre than 

 the primary synapticula, and similarly the tertiary endosepta are joined to the adjacent 

 exosepta by synapticula still further from the centre and forming an outer ring. 

 Thus there is only one synapticular bar in each interseptal loculus. In longitudinal 

 section the synapticula are seen to be narrow curved bars or partitions, in shape and 



