PLATE IV. 
Platyceras fornicatum. 
Page 11. 
Figs. 1-3. Dorsal, posterior and lateral views of one of the typical specimens, showing the strong ridge or 
fold of the left side and the bases of strong spines. Schoharie county, N. Y. 
Figs. 4, 5. Dorsal and lateral views of a specimen partly defiuded of shell, showing a more pointed beak, 
less distinct carina and more numerous spines. Williamsville, N. Y. 
Figs. 7, 8. The aperture and upper side of a large specimen, similar in character to fig. 1; somewhat 
crushed, but with a deep strong notch or sinus in the lip, corresponding to the carina, 
imperfectly seen in fig. 7. Onondaga, N. Y. 
Figs. 18-20. Three views of a large individual, having the features of figs. 12-14, in the younger stages of 
growth, but becoming more expanded with age. The surface preserves a few scattered spine- 
bases. Onondaga, N. Y. 
Platyceras gymbium. 
Page 12. 
Figs. 9—11. Lateral, dorsal and posterior views of the typical specimen. This specimen is destitute of shell, 
except beneath the beak, and does not show the surface characters. 
Platyceras rictum. 
Page 13. 
Fig. 6. View of the aperture of a convex individual. Onondaga, N. Y. 
Figs. 12-14. Dorsal, posterior and lateral views of the typical specimen. This is entirely destitute of shell, 
but retains the imprint of surface markings on most parts. From the Hamilton group at Can¬ 
andaigua Lake, N. Y. 
Figs. 15-17. Dorsal, apertural and lateral views of a very depressed form, showing the surface markings. 
From the Upper Helderberg group, Onondaga, N. Y. 
