PLATE V. 
Platyceras echinatum. 
Page 13. 
Figs. 1, 2. Dorsal and lateral views of a small specimen, enlarged to twice the natural size, showing the 
characters of surface when exfoliated, leaving only the spine-bases remaining. From the 
Hamilton group at Ludlowville, Cayuga Lake, N. Y. 
Figs. 3, 4. Dorsal and lateral views, natural size, of a specimen denuded of the exterior shell and showing 
the bases of the spines as tubercles. From the Tullyj limestone at Ovid, N. Y. 
Platyceras dumosum var. rarispinum. 
Page 16. 
Fig. 5. Lateral view of a small specimen, showing a few scattered spines. Oneida county, N. Y. 
Figs. 6, 7. Lateral and dorsal views of a larger specimen, similar in character to the preceding. Darien, £L Y. 
Fig. 10. Oblique side view of a specimen which is partly imbedded in rock, and preserves several of the 
spines in place. Schoharie, N. Y. 
Platyceras fornicatum var. contractum. 
Page 12. 
Figs. 8, 9. Two views of the specimen referred to as a variety in the original description of P. fomimbum. 
Platyceras dumosum, Conrad. 
Page 14. 
Fig. 11. View of a small specimen preserving several spines and spine-bases. Falls of the Ohio. 
Fig. 12. View, of a larger and more robust specimen, partially imbedded in the rock, and showing numerous 
spine-bases. Schoharie, N. Y. 
Fig. 13. View of a specimen w'ith a large number of broken and displaced spines. From the Corniferous 
limestone near Columbus, Ohio. 
Figs. 14, 15. Two views of a large ventricose individual (the type specimen used by Mr. Conrad for descrip¬ 
tion), showing the bases of hollow spines, covering almost the entire surface. Schoharie, JST. Y. 
Fig. 16. The aperture of a long slender specimen, similar to tigs. 11 and 12. The surface shows numerous 
spine-bases, and a plicated margin. Helderberg mountains, N. Y. 
