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



I, this unilateral order of appearance is of no significance, par- 

 ticularly as later figures almost conclusively show that it is 

 simply a matter of unequal growth. It will be observed in 

 figure 9 that the septum marked (A) bears a relation to the 

 septum marked I in the lower left hand quadrant very similar 

 to the relation which septum number 2 in the counter quad- 



15 



Figure 15. Plan of the septa in a Zaphrentoid coral. 



rant of figure 15 bears to septum number 1. Likewise the 

 septum marked (A) in the upper left hand quadrant of figure 

 9 holds a relation with reference to the adjacent primary sep- 

 tum similar to that which number 1 in the left hand cardinal 

 quadrant of figure 15 bears to the adjacent transverse septum. 

 It will be remembered, also, that in the above explanation of 

 Duerden's figure 1, the comparative thinness of the upper pair 

 of septa marked I was pointed out and that this was consid- 

 ered to be suggestive. 



In figure 10 (figure 3 of Duerden, inverted) we observe a 

 further increase in the number of secondary septa. . Here the 

 comparative thinness of the lower pair of septa marked I is 

 again noticeable. In the upper quadrants are two secondary 

 septa marked (A), each lying adjacent to the upper lateral 

 "primary" septum on the side in which it appears. In the 

 lower quadrants are two new septa marked (A) and in the left 

 the beginning of a third, marked (B), which bears the relation 

 to (A) that the latter holds with respect to the adjacent sep- 

 tum marked I. In this figure we also notice the division of 

 the median septum into an upper and lower portion, the upper 

 part of which, in Duerden's figures, is marked the " cardinal," 

 the lower the " counter" ; i. e., in Duerden's diagram 3, the upper 



