PLATE XI. 
Platyostoma unisulcata var. 
Page 27. 
Fig. 1. Apertural view, showing the general form and elevation of the shell, the columella, etc. 
Fig. 2. The back of the same specimen, showing the angularity of the volution. 
Fig. 3. The spire. 
Platyostoma lineata var. sintjosa. 
Page 24. 
Fig. 4. Front view of a small specimen with a depressed spire. 
Fig. 5. Basal view, showing the deep sinus in the aperture. Hamilton group, Livingston county, N. Y. 
Figs. 6, 7. Apertural view and spire of a larger specimen, with much higher spire and rounded volutions. 
From the Hamilton group, Canandaigua Lake, N. Y. 
Fig. 8. Basal view of the same, showing the deep sinus of the lip. 
Platyostoma aplata. 
Page 20. ■ 
Fig. 9. The spire of an imperfect specimen. From the Schoharie grit, Schoharie, N. Y. 
Pleurotomaria ? sp.? 
Naticopsis? cretaeea, Hall. Illustrations of Devonian Fossils: Gasteropoda, pi. 11. 1876. 
Not Naticopsis cretaeea, H. & W. Twenty-third Rep. N. Y. State Mus. Nat Hist., p. 240. 1873. 
Not Naticopsis IcBvis, Meek. H. & \V. Ib. Explanation pi. 12, fig's. 3-5. 
Fig. 10. The spire of an imperfect cast referred with doubt to this species. 
Fig. 11. Front view of the same, showing the obliquity of the shell and the substance of the callus filling the 
umbilicus. Upper Helderberg limestone near Clarence Hollow, N. Y. 
Figs. 12, 13. Two views of an internal cast. Upper Helderberg limestone near Columbus, Ohio. 
Strophostyltts ttnicus. 
Page 30. 
Fig-. 14. Front view of the typical specimen, showing the columella and the form of the shell. 
Fig. 15. Summit view of the same specimen. From the Schoharie grit, Schoharie, N. Y. 
Strophostyltts varians. 
Page 31. 
Figs. 16, 17. Two views of a young, very oblique specimen, showing, in fig. 16, the peristome nearly detached 
from the body of the preceding volution—an exceptional feature. 
Fig. 18. Enlargement of the surface stria from a small, well-preserved specimen. 
Figs. 19, 20. Two views of a larger specimen, showing the peristome more completely united to the preceding 
volution. 
Fig. 21. A medium-sized specimen, showing very great obliquity of the last volution and a slight separa¬ 
tion of the peristome from the body-whorl. 
Figs. 22-24. Other examples, showing the form of the shell and the very broad umbilicus. 
Fig. 25. A small specimen, showing strong plications near the aperture, indicating- the existence of a notch 
in the peristome during the later period of its growth. 
Fig. 26. A large and more rotund specimen, showing an injury to the peristome during growth. 
Figs. 27, 28. Two views of a large, well-formed, rotund specimen. The second figure shows the obliquity 
of the outer lip to the axis of the shell. 
Figs. 29, 30. Two views of a large specimen, the latter showing the inner lip spreading over the preceding 
volution. 
Fig. 31. A large oblique specimen with the peristome much thickened. 
The specimens are all from the Upper Helderberg limestone, Onondaga county, N. Y. 
