PALEONTOLOGY 



PLATE XVI. 



Ptychoceras meekanum Whitf 457 



Fig. 1. Lateral view of a sijecimen preserving the curved extension of the smaller limb, and 



also showing the commencement of old age characters, in the closely arranged 



rings near the outer end of the larger limb. 

 Fig. 2. Diagram of a septum from just within the bend of a similar specimen. Enlarged 



to two diameters. 



Ptychoceras crassum Whitf 459 



Fig. 3. Lateral view of the specimen described, natural size. 



Fig. 4. Dorsal view of the same, showing the features of this part of the shell. 



Fig. 5. Diagram of a septum from another individual, enlarged to the same extent as Fig. 2. 



Fig. 6. Sectional diagram of the specimen, showing the thickness of the shell. 



Ancyloceras jenneyi Whitf 452 



Fig. 7. Lateral view of a specimen of the species, preserving an outer volution, and parts 



of the inner smaller coil. 

 Fig. 8. Dorsal view of the outer part of the same, showing the ranges of nodes, not exactly 



the same on the opposite sides. 

 Fig. 9. Diagram of a septum from near the middle of the larger coil. Two diameters. 



See also PL 15, Fig. 5. 



Nautilus dekayi var. montaislensis Meek 439 



Fig. 10. View of the inner side of a specimen, showing the breadth of the shell and the 



distance of the septa. 

 Fig. 11. Lateral view of the same specimen, showing the rate of increase in the coils. The 



apparent umbilical perforation arises from the exfoliation of the shell. 



