PALEONTOLOGY. 

 PLATE XV. 



Page. 

 Heteroceras newtoni Whitf 449 



Figs. 1, 2. Views of the opposite sides of the type specimen, showing the rapidly expand- 

 ing tube, and preserving the surface characters. 

 Fig. 3. Vertical view of the same individual, showing the broad umbilical opening and the 



commencement of the deflection of the outer end. 

 Fig. 4. Diagram of a septum from near the larger extremity of the specimen. Enlarged 



to two diameters. 



Ancyloceras jenneyi Whitf 452 



Fig. 5. Enlargement, to one and a half diameters, of a septum from a small fragment of a 

 specimen, showing some variations as compared with that shown on Plate 16, 

 Fig. 9. See also PL 16, Figs. 7-9. 



Heteroceras ? nebrascense M. &, H 451 



Fig. 6. Lateral view of a specimen referred to this species, showing two volutions of the 

 septate shell. See also PI. 14, Fig. 9. 



Ancyloceras tricostatus Whitf 454 



Fig. 7. Lateral view of the fragment, showing the triplicate character of the costse, and 



the obtusely triangular nodes on the dorsum. 

 Fig. 8. Enlarged diagram of a septum from near the commencement of the outer third of 



the fragment. Two diameters. 



