G. E. Gordon — Early Stages in Paleozoic Gorals. I lp.1 



having a Cjathophyllum ancestor, but that acceleration has 

 produced in one case a distinct type in which the Cjathophyl- 

 lum stage is either lost, or is of such short duration that it 

 escapes notice. 



In attempting to arrive at some definite conclusion as to the 

 ancestral condition of any fossil group, or as to whether any 

 particular plan of structure in fossil forms is a primitive one 

 or not, one must not ignore these facts so obviously illustrated 

 in many groups that have been carefully and successfully 

 studied. In the absence of proof that the specimens in hand 

 are primitive, or that they illustrate a primitive condition, of 

 which one must always be in doubt, one must in order to 

 meet the first requirements of a safe premise select a type 

 most likely to be primitive, and this must be done on the basis 

 of chronogenesis. A type occurring late in geological time, at 

 least a considerable time subsequent to the earliest occurrence 

 of a type at all similar, is likely to be far from primitive, in 

 all respects at least, and at all events is not a safe type for 

 study. But a specimen selected on the basis of its early 

 appearance in geological time may be presumed to give the 

 most primitive conditions which it is possible to obtain until 

 an earlier form which is favorable for study can be secured. 



Dr. J. E. Duerden has attempted to show by studies based 

 on Lophophyllum proliferum that it is unnecessary to " account 

 for a primitive tetramerism " in the Rugosa.* He would, on 

 the basis of his studies, consider the quadripartite symmetry as 

 a secondary development erected on a primitive hexameral 

 arrangement of the primary septa ; and by the development of 

 the secondary septa, according to his interpretation of the 

 primary condition, he finds the Rugosa, in so far as Z. pro- 

 liferum may be representative, most closely related to the 

 modern Zoanthese. In this paper I am not so much concerned 

 with establishing the relationship of the Rugosa as with dis- 

 cussing the probable number of the primary septa in these 

 forms. Certain studies which I have undertaken seem to 

 indicate that there is still good ground for believing that the 

 tetrameral plan is a primitive one.f Moreover, a careful study 

 of the diagrams in Duerden's paper has raised the question 

 if after all they may not illustrate a primitive tetrameral 

 arrangement of the main septa. 



It will be necessary in order to make as full a comment as 

 seems desirable on Duerden's studies of Lophophyllum to 

 reproduce a few of his figures. 



* Johns Hopkins University Circular, January 1902 ; Annals and 

 zine of Natural History, May 1902. 



f For valuable suggestions and criticisms in carrying on these studies the 

 writer is deeply indebted to Dr. Amadeus W. Grabau. 



