PLATE CXVIL 
Orthocekas duramen. 
Page 25. 
Fig. l.jA septate fragment, showing the rapid enlargement of the tube, and the depth of the air-chambers. 
Schoharie grit. Clarksville, N. Y. 
Orthoceras sceptrum. 
Page 26. 
Fig. 2. An individual preserving a large portion of the chambei’ of habitation and about thirty air-cham¬ 
bers. The specimen is an internal mould and shows an organic deposit in the air-chambers 
toward the apex where the walls have been dissolved. The organic deposit is represented by 
concavities in the filling of the air-chambers and increases in amount toward the apex. The 
marked curvature of the tube is apparently normal and not the result of compression. 
Upper Helderberg limestone. Cherry Valley, N. Y. 
TrOCHOCERAS (GoNIOCERAS ?) PANDUM. 
Page 37. 
Fig. 3. A specimen preserving ten air-chambers, showing four very shallow chambers at the larger ex¬ 
tremity and probably close to the chamber of habitation. 
Fig. 4. Id. Section showing the lentifoi’in transverse section of the tube. 
Fig. 5. The apical portion of an individual, showing the enlargement of the tube and the shallow air- 
chambers toward the apex, as mentioned in the description of the species. 
Schoharie grit. Albany county, N. Y. 
Orthoceras directum. 
Page 27. 
Fig. 6. An example preserving a large part of the chamber of habitation with twelve attached air-cham¬ 
bers. The suture lines are deeply impressed from weathering and the solution of the septal 
margins. 
Fig. 7. Id. Longitudinal sections, showing the septa to have been broken down and obliterated on the 
interior of the tube, notwithstanding the marked indications of septa shown on the exterior of 
the specimen. 
Corniferous limestone. Delaware, Delaware county. 0. 
