C. E. Gordon — Early Stages in Paleozoic Corals. 125 



represented by the curved line, which ridge was small and of 

 about the same size as the tertiary septa. 



As was stated above, the specimen was examined by the aid 

 of a binocular in electric light. No doubt was left in my 

 mind that the four septa indicated by the heaviest lines in the 

 figure extended farthest down into the base of the calyx. Not 

 content, however, with my observations, I submitted the speci- 

 men to two others, whose results tallied with mine. The 

 results, therefore, seemed to indicate that Streptelasma pro- 

 fundum showed a primary tetrameral arrangement and that 

 the further addition of the secondary septa proceeded in accord- 

 ance with the law that the Zaphrentoid type has been shown 

 to illustrate. 



In the criticism offered above of Duerden's figures I have, I 

 think, offered another possible interpretation of the occurrence 

 of one of the pairs of so-called primary septa in the tip of 

 Lophopliyllum proliferum. Whether this interpretation is 

 accepted or not, I think it is by no means established that the 

 hexameral arrangement is a primitive one. In the first place, 

 as I have pointed out ' above, L. proliferum is in some 

 respects, notably because of its occurrence in Carbonic time, 

 not a suitable specimen upon which to establish a primitive 

 arrangement of the septa. S. profxmdum from the Ordovicic 

 was selected for study mainly because of its early geological 

 occurrence. The fact that it shows a primary tetrameral 

 arrangement suggests that such was the primitive condition. 

 To my mind it suggests this because it is a comparatively old 

 type and, because, so far as the septal sequence is concerned, 

 it shows absence of acceleration. 



It is evident, I think, that the primitive condition of these 

 septa in the Rugosa is not yet settled. The tetrameral arrange- 

 ment, if primary, will so long as this is made the basis of clas- 

 sification, place those corals which possess it in a group by 

 themselves. No modern corals exhibit the peculiar septal 

 plan as revealed in Streptelasma profundumj nor, in fact, as 

 revealed in Lophopliyllum proliferum. The fact that Lopho- 

 phyllum is quite distinct from anything that is modern per- 

 haps gives some support to the view that it is merely an accel- 

 erated type of a Zaphrentoid coral, occurring as it does among 

 an extinct group. 



Whether the hexameral plan is derived from a tetrameral 

 one is still an unsolved mystery. Developmental studies 

 among modern forms may yet throw some light on this ques- 

 tion. 



From the wide prevalence of the tetrameral arrangement 

 among the extinct Rugosa it is probable that it is something 

 inherent rather than acquired by mode of growth, especially 



