PLATE III. 
Plattceras (Orthonychia) attentjatum. 
Page 6. 
Fig-. 1. Dorsal view of a small specimen which has been laterally compressed. 
Figs. 2, 3. Dorsal and lateral views of a more expanded specimen, showing strong folds near the margin. 
Fig. 4. Lateral view of the specimen fig. 1, showing the folds of the margin. 
Figs. 5, 6. Lateral and dorsal views of an unusually expanded specimen, showing irregular pustulose ridges 
on the surface of the expanded portion. 
Plattceras bucculentum. 
Page 10. 
Fig. 7. Lateral view of a specimen which may be the young of P. bucculentum, but has the appearance of 
an adult shell. From Canandaigua Lake, N. Y. 
Platyceras atjriculatum. 
Page 7. 
Figs. 8-10. Dorsal, rig-ht and left views of a specimen, showing the form of the shell and the lateral expan¬ 
sion, with its ridges. Darien, N. Y. 
Plattceras Thetis. 
Page 8. 
Figs. 11, 12. Left and right lateral views of a small specimen, showing the narrow form and enrolled beak. 
Figs. 13, 14. Left and right lateral views of an unusually large specimen, showing a more strongly arcuate 
form. 
Figs. 15, 16. Left views of two specimens of large size, showing some variation in form. From the Ham¬ 
ilton group at Canandaigua Lake and Bellona, N. Y. 
Plattceras symmetricum. 
Page 9. 
Fig. 17. Lateral view of a large specimen, referred with some' doubt to this species. From the Hamilton 
group, Canandaigua Lake, N. Y. 
Figs. 18-21. Four views of one of the typical specimens exhibiting the general features of the species. Fig. 
20 shows the symmetrically coiled beak. Fig. 21 is accidentally compressed on one side. 
From Canandaigua Lake, N. Y. 
Figs. 22-24. Three views of a specimen, showing a loosely coiled beak (except at the apex) and strongly 
plicated margin. 
Fig. 25. Dorsal view of a specimen, showing a strong anterior fold. From Canandaigua Lake, N. Y. 
Plattceras bucculentum. 
Page 10. 
Fig. 26. Lateral view of a specimen, showing the folds of the shell on the left side. 
Fig. 27. Dorsal view of an individual, showing the strong lateral folds. 
Fig. 28. Dorsal view of the specimen fig. 26. 
Fig. 29. The aperture of a large symmetrical specimen, showing a fold in the posterior margin. Livingston 
county and at Canandaigua Lake, N. Y. 
Plattceras Thetis? var. subspinosum. 
Page 9. 
Fig. 30. View of a. large flattened specimen, possessing many of the features of P. Thetis, but more robust 
and with the aperture contracted on the right side and strongly plicated. There are a few short 
spines at the summit of the volution. From the Hamilton group at Canandaigua Lake, N. Y. 
