UHEDE : SEMINULA ARGKNTIA. 157 



tachment of the spiralia. Such structures must certainly vary in 

 order to support the spires in their various positions. 



The above facts would seem to indicate the following conclusions : 

 First, in those spire-bearing brachiopods in which the form of the 

 shell does not govern the position of the spires, the Athyridse in par- 

 ticular, the spires may be subject to a considerable variation in both 

 position and form. Second, that the crural supports are probably so 

 modified as to accommodate the spires in their various positions. 



In the light of the foregoing, it will be seen that in the future it 

 will be necessary to study the structure of several specimens before 

 using small variations of internal structure in these shells as bases 

 for group divisions. 



One might expect greater individual variation among the Flint 

 Hills specimens, owing to the physical changes that were taking place 

 during the close of the Carboniferous and the early Permian ; changes 

 which soon caused this species, together with many others, to become 

 extinct. However, this cannot be said of the most striking case 

 ( No. 11) from the Topeka limestone. It would seem that such varia- 

 tions as are found in Nos. 3 and 11 would be decidedly detrimental to 

 the well-being of the animal, though the latter of the two seems to 

 have been a vigorous individual. 



Indiana University, Bloomikgton, 

 April 8, 1902. , 



