EXPLANATIONS OF PLATE 16 (7). 



Trochoceras coBTATtJM. page 360. 



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

 *' 2. Section showing the convexity of the septa and the position of the siphuncle. 



Cyrtooeras RiQiDtTM. page 358. 



Figs. 3, 4. Lateral and dorsal views of the outer portion of the cast, showing the cur- 

 vature of the shell and the character of the undulating ridges. 

 " 5. Transeverse section, showing the forna. 



LiTuiTEs MARSHTi. page 362. 



Fig. G. Lateral view of a specimen natural si2e, showing the oblique costae and the 

 outline of the septa. 

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

 position of the siphuncle. 



Trochoceras desplainense. page 359. 



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

 in the rock, showing the strong oblique costae. 

 " 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. 



Ctrtoceras fosteri.: page 349 (45). 



Figs. 11, 12. Lateral and dorsal views of the specimen described. 

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

 siphuncle. 



