PLATE XXVII. 



Zone of Aegoceras armatum. 



Fig. 1. Aegoceras scbmuticum, Oppel. Lateral view, natural size, showing the 



regularity of the ribs and smallness of 

 the tubercles ; likewise the small amount 

 of the involution of the last whorl. My 

 collection. 

 2. — — — Front view of the siphonal area, showing 



the tubercles in profile, the squareness 

 of the siphonal area, and the numerous 

 small ridges that cross the area between 

 the larger folds. 



