PLATE XVIII. 



GOMPHOCERAS SCRINIUM, HaLL. 

 Page 410. 



Fig. 1. Lateral view of the outer chamber, the lower end showing the concavity of the septa. 

 " 2. View of the aperture of the same individual. 



" 3. A transverse section of another individual, showing the size and position of the siphuncle, 

 with muscular or vascular markings at the margin. 



Cyrtocebas laterals. Hall. 



Page 407. 



Fig. 4. Dorsal view of a specimen, showing septa and preserving the remains of faint longitudinal 

 ridges. 

 " 5. Lateral view of the same individual. 



" 6. The outer circle of the figure represents the form of section and the position of the 

 siphuncle of this species, — the inner portion that of C. lucillum. 



Cl'RTOCERAS LUCILLUM, HaLL. 

 Page 406. 



Fig. 7. Lateral view of a specimen of this species. The figure is somewhat restored. See inner 

 portion of figure 6 for transverse section. 



GiRTOCERAS BREVICORNE, HaLL. 

 Page 407. 



Fig. 8. Lateral view of the specimen described. The specimen consists of the filling of the outer 

 chamber and the matrix of the lower part, which has been represented from a cast 

 in the cavity. 

 " 9. Dorsal view of the same. 



Orthoceras abnorme. Hall. 



Page 415. ' 



Fig. 10. View of a specimen of this species having the filling of the chambers in the lower part 

 broken away, showing the siphuncle, and the inner core with its numerous ramifica- 

 tions uniting with the walls of the siphuncle. The view is taken looking obliquely 

 upon the specimen, so that the real amount of curvature is not observable. 



