314 ASSINNIBOINE AND SASKATCHEWAN EXPEDITION. 



one on the left is larger than the other, and again deeply 

 divided into two bifid and deeply sinuous branchlets. 

 The inferior lateral lobe is much smaller than the superior, 

 and very irregularly divided into two or three alternating 



Diagram of one of the septa of Ammonites Barnstoni. 



unequal lateral branches on each side, and one terminal 

 branch, with numerous sinuosities. The ventral lobe is 

 very small, and simply digitate. 



This species bears considerable resemblance in form, 

 and in the size and character of its umbilicus, to the 

 Jurassic species A. irens, D'Orbigny (Pal. Franc, tome i. 

 p. 562, pi. 222), but differs in having the costee pinched 

 up into little subnodose prominences around the umbilicus, 

 and bifurcating on the sides ; they are also much more 

 arched in passing over the dorsum. It is quite different 



