C. E. Gordon — Early Stages in Paleozoic Corals. 115 



The arrangement and order of appearance of the septa in 

 the Zaphrentoid coral, as generally accepted, is illustrated in 

 figure 15 ; (A) is the "cardinal" septum; (g) the "counter" 

 septum ; (s) the " alar " septa. The radiating lines indicate 

 septal margins as they appear on the surface of the corallum 

 when viewed from below. By the figure it will be seen that 

 in the cardinal quadrant the septa first to appear take a posi- 

 tion next the alar septa. In the counter quadrants the first to 



Figures 8, 9, 10 and 11. Figures 1, 2, 3 and 4 of Duerden, inverted. 



appear take a position next the counter septum. Let us care- 

 fully examine Duerden's figures to see if in any way they may 

 reveal traces of a tetrameral arrangement of the septa accord- 

 ing to the law apparent in the development of the septa in the 

 Zaphrentoid coral as above explained. 



By referring to figure 9, which it will be remembered is 

 Duerden's diagram (figure 2) inverted, we observe the appear- 

 ance of two secondary septa, each marked A, apparently as a 

 unilateral pair. I have already remarked that this appearance 

 as a unilateral pair may be explained on the principle of 

 unequal growth. Since we are concerned only with their rela- 

 tion to the septa, marked in the figure by the Roman numeral 



