552 



GEORGE H. GIRTY 



or we might say, as Professor Schuchert does, that two species 

 representing different sections of the genus Spirifer belong to 

 different phyla, and so on. Or, on the other hand, we might say 

 that two genera, such as Spirifer and Athyris, belong to different 

 pyhla, the one to the Spiriferoid stock, the other to the Athyroid. 

 The meaning of the word depends largely on the viewpoint of the 

 occasion, and any conclusion based on phyletic relationship is 

 almost nil unless the writer defines what he means by phylum. 



But let us consider what the force of such an argument really 

 is in general terms. Put case that there are two Spirifers having 

 other characters identical but differing in the height of the area 

 or the length of the cardinal line or other similar characters and 

 belonging to different phyla in the narrowest sense. We do not 

 distinguish them as different genera or even different species, but 

 say that these differences concern minor characters in which expe- 

 rience has shown that individual specimens differ from one another 

 and vary at different stages of their growth. Put case again that 

 we have two Spirifers, one with simple fold and sinus and pustulose 

 sculpture, the other with plicated fold and sinus and finely reticu- 

 late sculpture, the two belonging to different phyla, in a broader 

 sense. Here, again, we do not say, as Professor Schuchert does, 

 that these species belong to different genera because they present 

 important differences and have different phyletic relations, for 

 the characters which they possess in common are such as we recog- 

 nize as characteristic of the genus Spirifer and the differences are 

 such as experience has shown to be useful only in specific dis- 

 crimination. Again, suppose we have two generally similar oval 

 brachiopods, one with internal spires, the other with an internal 

 loop, and belonging to different phyla, in a still broader sense. 

 We do not refer these types to different genera because they show 

 such and such differences and belong to different phyla, for the 

 differences are more important than those by which genera are 

 determined and we place the species in still more widely separated 

 groups. In other words, in such cases as these phyletic relation- 

 ship enters little, if at all, into the determination of taxonomy. 

 We go straight to the intrinsic characters of the form and accord- 

 ing to the nature and degree of its resemblances and differ- 



