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



septum occurring on the concave side. Since we find not only 

 the fossula, but also the pinnate arrangement of the septa, 

 occupying the position of the lower portion of the median sep- 

 tum in Duerdens figures, this portion must be the cardinal, 

 which in this specimen is on the concave side ; and the upper 

 portion is the counter instead of the cardinal, as Duerden has 

 designated it. That this interpretation is correct is clearly 

 shown by the figures. We have now simply to invert the 

 diagrams to get a well organized Zapbrentoid type, in so far as 

 the adult arrangement of septa and fossula are concerned. 

 It remains yet to consider tbe two upper " primary " septa 



Certain studies 



of Duerden's figures in more careful detail 



13 



14 



Figures 13 and 14. Figures 6 and 7 inverted. 



which I have made on Streptelasma jprofundum from the 

 Black River limestone seem to indicate most strongly a tetra- 

 meral plan of growth in the primary septa of the Rugosa ; to 

 use a borrowed phrase, " in so far as this type may be taken as 

 representative." These studies will be given in greater detail 

 presently. Their significance here, however, is to indicate 

 that the tetrameral arrangement is not a secondary develop- 

 ment on a hexameral basis, but on the contrary, that the hex- 

 ameral arrangement in the tip of Lophophyllum is really only 

 apparent and that L. proliferum from the beginning exhibits 

 a quadripartite plan of the septa. To one who examines 

 Duerden's figures the hexameral plan at first sight seems to be 

 the only way of interpreting this very early condition. And I 

 am well aware that by some it is likely to continue as the only 

 interpretation. 



Jakowlew came to the important conclusion that the prim- 

 ary spaces in which the secondary septa did not develop 



