G. E. Gordon — Early Stages in Paleozoic Corals. 119 



appeared adjacent to the counter septum without regard to 

 whether the latter appeared on the convex or concave side of 

 the polyp.* In so far as Jakowlew's careful comparative 

 studies are conclusive this would again indicate that what 

 Duerden has designated as the cardinal septum is really the 

 counter septum, as I, by comparison with a typical Zaphrentoid 

 arrangement above, have pointed out to be the case. 



By an examination of the diagram of the adult we are 

 further impressed with the fact that the so-called primary 

 spaces in which secondary septa do not develop are at the time 

 of maturity not to be distinguished in any respect from the 

 spaces which separate the secondary septa in the same quad- 

 rants. We note also that the lateral septa marked I in the 

 upper quadrants of Duerden's figures have a position and an 

 order of appearance which, if they were to be regarded as sec- 

 ondary septa, would correspond to the septa marked by the 

 Arabic numeral 1 in the counter quadrants of figure 15, which 

 illustrates the usually accepted order of appearance in the 

 Zaphrentoid coral. We are furthermore impressed by the 

 fact that the later sections of the corallum (figures 1 and 14) 

 show the appearance of the tertiary septa, in the two Ram- 

 mem next the " cardinal " (Duerden) at the top of figure 7, 

 having precisely the same relations to adjacent septa as do the 

 tertiary septa in ail secondare Kammern. The tertiary septa 

 may have no sequence value, but the fact that they appear at 

 all in the " primary " interspaces next the " cardinal" septum 

 is suggestive that these spaces do not differ essentially from the 

 secondary interspaces. 



I am aware that in support of the interpretation which I 

 shall presently present as an explanation of the presence of 

 this pair of so-called primary septa next the "cardinal" sep- 

 tum, I have no absolute proof. I have called the reader's 

 attention to the striking resemblance which Duerden's dia- 

 grams have to the usually accepted arrangement and order of 

 appearance of the septa in the Zaphrentoid coral when the 

 diagrams are inverted and their structural features interpreted 

 in the terms of Zaphrentis. In Streptelasma (figure 16) it 

 w r ill be seen that the tertiary septa are present also in all inter- 

 spaces. As to any sequence in their order of appearance, it was 

 not possible to determine in the specimen, as their lower ends 

 were very thin, and the extent to which they went down into 

 the calyx could not be traced. The lines representing the ter- 

 tiary septa in figure 16 do not indicate their indistinctness at 

 their lower ends. 



With regard to the " ultimate fate of the two bilateral pairs 

 of primary septa " Duerden expresses himself as follows : 



*Ueber die Morphologie tmd Morpliogenie der Rugosa," Seite 412. 



