PLATE XVI. 

 Trochoceras notum, Hall. 



Page 403. 



Fig. 1. Dorsal view of a fragment of this species. 

 " 2. A septum showing its convexity and the position of the siphuncle. 



Gtrtoceras rigidvm, Hall. 



Page 408. 



Fig. 3. Lateral view of the outer portion of the cast, showing the curvature of the shell and the 

 character of the undulating ridges. 

 " 4. Dorsal view of the same. 

 " 5. Transverse section, showing the form. 



LiTUITES MARSBII, HaLL. 



Page 404. 



Fig. 6. Lateral view of a specimen of the natural size, showing the oblique costse and the out- 

 hne of the septa. 

 " 7. Profile showing the flattened dorsum, the concavity of the septa and the position 

 of the siphuncle. 



Trocboceras desplainense, M' Csesnet. 



Page 401. 



Fig. 8. View of the upper side of spire, taken irom an impression in the natural mould in the 

 rock, showing the strong oblique costee. 

 " 9. Dorsal view of the outer part of the last volution, showing the sinus in the margin of the 



aperture. 

 " 10. Transverse section, showing the convexity of the septa and position of the siphuncle. 



Cyrtoceras fosteri. Hall. 



Page 406. 



Fig. 11. Lateral view of the specimen described. i 



" 12. Dorsal view of the same. 

 " 13. Transverse section, showing the convexity of the septa and position of the siphuncle. 



