PLATE VII. 
Platyceras undatum. 
Page 17. 
Figs. 1, 2. Views of the opposite sides of an internal cast, showing transverse lines of broad tubercles, and 
giving the general form of the shell. The original shell has doubtless been marked by strong- 
spines. 
Platyceras dumosum, Conrad. 
' Page 14. 
Fig. 3. Dorsal view of the specimen represented on Plate V, fig. 16. 
Platyceras nodosum. 
Page 17. 
Figs. 4, 5. Lateral and dorsal views of an internal cast, showing very strong tubercles, indicating spine-bases 
in a somewhat quincunx arrangement; 
Platyceras crassum. 
Page 18. 
Fig. 6. View of an internal cast which is probably of this species. Schoharie, N. Y. 
Fig. 7. A somewhat smaller individual which is more expanded toward the aperture, partially from com¬ 
pression. Clarksville, Albany county, N. Y. 
Figs. 8-10. Three views of the typical specimen which is a partial cast and shows great thickness of shell. 
Helderberg mountains, N. Y. 
