SUMMARY 



OF 



DEVELOPMENTAL CHANGES 



SIZE AND CONTOUR. Although the species described in the pre- 

 ceding pages present a wide variation in form and general appearance, 

 the nature of the changes which take place in the development of the 

 shell is remarkable in its uniformity. 



In nearly every species, the inceptive state is represented by a 

 shell having a subcircular outline, with valves of slight convexity. This 

 phase usually disappears before the individual reaches a length of i mm., 

 after which the specific characters are assumed, and are progressively 

 emphasized with each succeeding increment. 



On comparing the incipient stage in these fossil shells with that 

 of recent brachiopods, as given by Mr. E. S. MORSE for Terebratulina, 

 and by Mr. W. K. BROOKS for Glottidia, we find that, in respect to actual 

 size, there is a slight, though perhaps unessential difference. At the 







earliest stage of growth figured by MORSE,* the shell has a length of 

 about .3 mm. and in the next stage represented, of approximately .6 mm. 



* Memoirs of the Boston Society of Natural History, Vol. ii ; On the Early Stages of 

 Terebratulina septentrionalis, pi. I, figs. 2, 3. 1869. 



