Report of the State GEOLOGIST. 



471 



and Obolus, and the early growth Btages of many genera 

 where the pedicle is long and flexible, produced in the 



vertical axis of the animal, and at the 

 same time not restricted in its passage to 

 one valve, the differences in the form of 

 the two valves are at their minimum, as 

 they are more equably exposed and resist- 

 ant to externa] physical impacts. Where 

 there is a decided inequality in the valves, 

 it has been observed in living forms, 

 and is probably equably true ot fossil 

 species, that the pedicle is short, rigid 

 and restricted to one valve ; and there 

 thus appears to be a certain definite rela- 

 tion between the angle at which the 

 pedicle is protruded and the size of the 



Fio. 19.— Lingula Murphiana. Fig. 20.— Athyris subtilitn. Fig. 21.— Orthis biloba. 



(Davidson.) 



( valves. The pedicle-valve, which, typically, in the adult 

 condition is the larger, is the seat of the principal muscular 



Figs. 22 and 23. — Spirifer angitstu*. 



Figs. 24 and 25.— Pentagonia unisulc«t<i . 



activity and the main lodgment of the viscera; it is, in 

 a certain sense, the cell of habitation of the animal, and 



23 



