PLATE II. 



Platyceras (Orthontchia) pekplexum. 



Page 4. 

 Figs. 1, 2. Views of the opposite sides of a specimen, showing the form and the irregular plications. 

 Kgf. 3. Lateral \new of a compi-essed specimen, imperfect at the apex, showing the plicated surface and 

 concentric stiite. 



Platyceras erectum. 



Pago B. 



Tig. 4. View of the origrinal specimen figured and desci-ibed in the Fourth District Report. Upper Helder- 

 lierg limestone, five miles east of Buffalo, N. Y. 



Figs. 5, 6. Lateral and dorsal views of a specimen, showing a sudden expansion of the shell at the end of the 

 lii'st volution. Fi-om Cayuga, C. W. 



Figs. 7, 8. Two views of a specimen, with less closely coiled beak. From the Hamilton gi\5up at Pavil- 

 ion, N. Y. 



Figs. 9, 10. Views of the opposite sides of a larger curved specimen. From the Hamilton group at Gen- 

 eseo, N. Y. 



Fig. 11. Lateral view of a small specimen, with closely coiled apex. Fi-om the Hamilton group. 



Platyceras carinatum. 



Page 5. 

 Figs. 12, 13. Lateral and dorsal views of a small specimen. Upper Helderberg limestone, Helderberg 



mountains. 

 Figs. 14-T6. Three views of a specimen. From near Williamsville, N. Y. 

 Figs. 17-19. A large internal cast, showing several plications on the right side. From the Ujjper Helderberg 



group, Sandusky, Ohio. 

 Figs. 20, 21. Two \-iews of a specimen. From the Hamilton group at Canandaigua Lake, N. Y. 

 Figs. 22-25. Views of a vei-y perfect specimen, fi'om the same locality as the preceding. 

 Fig. 26. Posteiior jirofile view of a large individual, showing an elevated obtuse caiination along the back 



of the shell. From Bellona, N. Y. 

 Fig. 27. Lateral view of the same, showing plications on the left side, with the sinuosities and projections of 



the margin indicated by the direction of the suiface stiise. 

 Figs. 28, 29. Dorsal and lateral views of an internal cast, showing decided lobations on each side of the 



shell, and the carination in the center. Helderberg mountains, N. Y. 



• 



Platyceras conicum. 



Page 3. 

 Figs. 30, 31. Lateral and upper views of an extremely carinate individual, with a regularly arcuate obtusely 

 pointed apex. From Onondaga county, N. Y. (Reference to these figures is omitted in the text.) 



