PLATE X. 
Platyostoma lineata. 
Page 21. 
Fig-. 3. A small patulose specimen. From the Upper Helderberg group, Onondaga county. 
Fig. 2. The aperture and spire of a symmetrical specimen,, having the normal characters of the species. 
Figs. 3, 4. Summit of the spire and lateral view of the specimen fig. 2. 
Figs. 5, 6. The spire and aperture of a larger specimen, differing from the preceding in the curving of the 
columella. 
Fig. 7. The spire of a specimen of medium size, which, during a part of its growth, has possessed a slit in 
the outer lip, occurring, apparently, from some accidental cause, at the commencement of the 
outer volution, and afterwards becoming- closed, has left the- surface plicated and irregular. 
Upper Helderberg group, Schoharie, N. Y. 
Fig. 8. The spire of a large individual of the ordinary form of the species, as it occurs in the limestone. 
Fig. 9. A similar view of a more l-obust individual. 
Fig. 10. Lateral view of the outer volution of a specimen similar to figure 9. 
These specimens, with two exceptions, are from the Upper Helderberg limestone at "Williams- 
ville, N. Y. ; they preserve, in a well-marked manner, the concentric and radiating striae. 
Fig. 11. The spire of a specimen somewhat similar to fig. 7. 
Fig. 12. Enlargement of the surface striae of the same. Hamilton shales, near Geneseo, N. Y. 
Figs. 13, 14. Two views of a specimen, preserving the surface in great perfection. The specimen is slightly 
depressed from accidental causes. From the Hamilton shales, Canandaigua Lake. 
Fig. 15. Enlargement of the surface of the preceding. 
Figs. 16-18. Three views of a large specimen, preserving the form of the aperture and peristome. The 
aperture is slightly rhomboidal, varying somewhat from the prevailing type. From the Ham¬ 
ilton shales at Canandaigua Lake. 
Fig. 19. An unusually large individual, which preserves the strife of growth very distinctly, while the con¬ 
centric striae are obsolete. Corniferous limestone, Darien, N. Y, 
Figs. 20, 21. Two views of an internal cast of the same species. Chemung group. 
Platyostoma lineata var. callosa. 
Page 23. 
Fig. 22. The aperture of a specimen which has the appearance of P. lineata, but with a thickened callus on 
the inner lip. 
Fig. 23. The spire of the same specimen.. 
Platyostoma defigurata. 
Page 24. 
Fig. 24. The apertural side of the specimen of which the outer volution has been crushed. 
Platyostoma lineata var. ampla. 
Page 23. 
Fig. 25. The spire. 
Fig. 26. The apertural side, showing the great elevation, large aperture and peculiarity of the columella, 
approaching in character to Strophostylus. 
Platyostoma eitomphaloides. 
Page 25. 
Fig. 27. Dorsal view of the specimen. Hamilton group, York, Livingston county, N. Y. 
Fig. 28. The base of the specimen, showing the aperture and the columellar lip modified by the preceding 
volution. 
Fig. 29. The spire as seen from above, showing the depressed upper surface of the outer volution. 
