230 



Prof. J. E. Ducrdcn on the 



Fi-. 1. 



Fig. 3. 



Fig. 1. — Lophophyllum prolxferwn (Septal Sequence, Figs. 1-8). Trans- 

 verse section immediately above the tip of a corallum. The lines of 

 calcitlcation of six primary septa (protosepta) are clearly seen, those 

 of the two median septa being continuous. At this level all the 

 septa are thickened to such a degree that there are no interseptal 

 spaces remaining, and in such a surface view as that from which the 

 figure was taken there is no indication of the boundary surfaces 

 between two adjacent septa. According to the accepted terminology, 

 the upper border is dorsal and the lower ventral. 



Fig. 2. — Section above that of Fig. 1. An interseptal chamber, repre- 

 sented by the black wedge-shaped areas, now occurs between all the 

 septa. The lines of calcification of an additional pair of septa 

 (metasepta, a, a) are seen, situated within the two middle of the six 

 priuiary interseptal chambers (the counter quadrants of palamnto- 

 logists). The number of external ridges and grooves is double the 

 number of internal septa, a septum corresponding with each alternate 

 groove. 



Fig. 3. — Section above that of Fig. 2. A pair of raeta>:epta (rt,, </,) has 

 now appeared within the two ventro-lateral of the six primary 

 interseptal spaces (tlie prinei])al or chief quadrants), corresponding 

 with the metasepta (n, «) of the middle primary chambers. 



Fig. 4.— A section still higher. .\nother pair of septa (i, />) is now 

 appearing within the two middle primary chambers. At first tlie 

 new septa are sharply turned toward.^; the older septum on their 

 dorsal aspect and there is no interseptal space. 



