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



ag it is characteristic not only of bent forms but also of simple, 

 straight cones. At all events, one may take exception to the 

 statement that "studies on the septal development of extinct 

 Paleozoic corals reveal that in these early forms the primary 

 septal plan was hexameral like that of modern forms." 



Further studies upon well-preserved specimens of early 

 Rugosa are much to be desired. 



Postscript. 



Since writing this article I have received and carefully read 

 an excellent paper by Dr. Duerden on " The Fossula in Ru- 

 gose Corals." In this article I find a full recognition of the 

 principle of retardation in development. The author shows 

 beyond question that the alar fossulae and the cardinal groups 

 of shortened fused septa in Hadrophyllum are developmental 

 stages when compared with the ephebic condition of a form 

 like Streptelasma. Since retardation in development means 

 the retention in the adult stage of characters which belong to 

 earlier stages, nepionic or neanic, Hadrophyllum must be a 

 retarded type when compared with a form like Streptelasma, 

 which passes through a Hadrophyllum stage. Both forms are 

 probably to be regarded as derived from a protostreptelasmic 

 stock. 



The author of the paper makes the point that, 



" Whenever alar fossulae are present they represent an incom- 

 pletion in the establishment of the newer septa of the alar region 

 as compared with species in which no alar fossulse are repre- 

 sented ; they have only a developmental significance and would not 

 correspond with any structural peculiarity of the fully devel- 

 oped polyp."* 



This is the point which I have insisted upon with reference 

 to the pair of so-called " primary septa" in L. proliferum / 

 namely, that they do not have the structural importance which 

 Duerden gives to them, but that they have a developmental 

 significance only. 



Duerden further remarks : 



"As would naturally be expected from such an explanation 

 even individuals of the same species may vary much with regard 

 to the presence or absence of alar fossulae." f 



This is evidently true. The only exception one might take 

 to such a statement is the propriety of calling the variations 



* " The Morphology of the Madreporaria, VI, The Fossula in Eugose Cor- 

 als," p. 33. 

 flbid., p. 33. 



