THE GENUS SYRINGOPLEURA SCHUCHERT 553 



ences determine the order of its taxonomic relationship to other 

 organisms. 



On the other hand, let us suppose a rare case in which two forms 

 are closely alike in most, or even all, of their mature characters but 

 at the same time they can be shown to belong to different phyla. 

 In this instance phyletic relationship has pre-eminent importance. 

 We cannot place the two types in taxonomic relationship more 

 close than the most remotely related of their ancestors. They 

 must be placed in different genera (at least) if that phyletic rela- 

 tionship is generic ; in different families if it is familiar ; in different 

 orders if it is ordinal, and so on. The logic of the situation seems, 

 then, really to be that the phyletic argument only sets a limit on 

 how close two types may stand in taxonomy, but does not enter 

 into the determination of how far apart they may stand. That is 

 based upon the physical characters of the mature individuals, not 

 upon development or on the theories of investigators. 



Returning now to the case of Syringothyris and Syringopleura, 

 we find that the reputed ancestor of Syringothyris and the reputed 

 ancestor of the suppositious Syringopleura are different species 

 of the genus Spirifer. The phyletic argument, 1 if used aright, 

 proves not that they must belong to different genera, but that they 

 cannot be placed in the same species. If we base a determination 

 of the relationship of Syringothyris and "Syringopleura" on their 

 real, as distinguished from their speculative, characters, it would 

 appear that they should be regarded as specifically, but not generi- 

 cally, distinct. At least, the peculiarities which are thought to 

 distinguish Syringopleura are only rated as of specific import in 

 the true Spirifers, and I do not see why they should be more impor- 

 tant in the closely related syringophorous shells. 



Therefore, it appears to me that Syringopleura is based on a 



1 The phyletic (phylic would be a much better term, but it unfortunately lacks 

 authority) argument, which really only serves as a check upon misleading or misunder- 

 stood direct evidence, to prevent two forms from being classed in too close zoological 

 categories, can rarely be used in paleontologic work because the phyletic relationship 

 is seldom, if ever, more than speculative. Even if the trend of the evidence were 

 correctly presented by him, the example set by Professor Schuchert in his proposed 

 genus Syringopleura is fraught with danger, since it would make our zoologic classifi- 

 cation the prey of all sorts of theories, however ill-considered. 



