PLATE CXVIII. 

 Okthoceras rudens. 



Page 28. 

 Fig. 1. A j >< >t-t i • pi : of the chamber of habitation, showing the numerous regular annulations of the tube 

 and the longitudinal stria 1 of the test. 



Hamilton group? Livingston county, N. Y. 



Okthoceras expositum. 



Page 29. 

 Fig. 2. An imperfect individual preserving 1 the greater part of the chambered portion of the tube, and 

 portion of the chamber of habitation. 



Iron ore bed of the Chemung group. Canton, Bradford county, Pennsylvania. 



Orthoceras consortale. 



Page 29. 

 Kig. '3. The air-chambers and lower portion of the chamber of habitation, showing the enlargement of 

 the tube and the depth of the air-chambers. Some traces of the surface markings are pre- 

 served on different parts of the tube. 

 Pig. 4. Id. A natural longitudinal section of five air-chambers, showing the monilifonn sipluincle and 



the rays on the upper bead at its contract with the septum. 

 Fig. a. Id. A septum showing the pnsiti.ui of the siphuncle, and exhibiting the effects of a slight com- 

 pression of the tube. 



Chemung group. Near Panama, Chautauqua county, N. Y. 



Orthoceras Indianensis. 



Page 30. 

 Fig. ti. A longitudinal section of three air-chambers, showing the small passage made by the siphuncle 



through the septa, and the reflection of the margin indicating a moniliform siphuncle. 

 Fig. 7. A fragment showing the enlargement of the tube, and depth of the air-chambers. 

 Fig. 8. The chamber of habitation showing its extent, and a broad constriction near the aperture. 

 Fig. 9. Id. The last septum showing the position of the siphuncle. 



Fig. 10. A fragment showing the characters of the r.rganic deposit on the walls of the air-chambers and 

 septa. 



Goniatite limestone. Rockford, Indiana. 



Orthoceras Icarus. 



Page 31. 



Fig. 11. The chamber of habitation with four attached air-chambers, showing the form of the tube and 

 tie- depth of the chambers. 



Fig-. 12. Id. Septum showing the position of the siphuncle, and the circular transverse section of the tube. 



Fig. 13. Longitudinal section of a chambered fragment showing the passage for the siphuncle through the 

 septa. 



Fig. 14. An enlargement to two diameters of the interna] mould of a small imperfect specimen, to show 

 the concave walls of the air-chambers from the solution of an organic deposit, and a line of 

 nodes indicating the ventral side of the tube. 



Kig. 15. A septum of another individual enlarged two diameters, showing an elevated areola with a fur- 

 rowed margin surrounding the siphuncle. produced by the solution of the organic deposit on 

 the septum. ^ 



Goniatite^limestone. Rockford, Indiana. 



