522 



Forty-fifth Report on the State Museum. 



is so frequent among the terebratuloids ; but in several general 

 Meristina, Kayseria, Bifida, a high median septum rises so close 

 to the angle of the jugum that but a very slight depression of the 



Fig. 166.— Brachial apparatus of Zygoapira modesta, showing the variation in the position of 



the jugum. 



entire brachial apparatus would cause it to rest upon the septum 

 and thus secure an efficient support. Whether this septum lias 

 been at all concerned in the modifications to which the spiralis 



FlG. 167.— Jugal processes of an adult Atri/pa reticularis. 



have been subjected in growth has yet to be determined. In 

 genera, where the spirals arc oonvergenl rather than divergent, 

 A try pa, Zygospira, G-lassla etc, the jugum is always simple in 



71 



