PLATE CXVIII. 
Orthoceras rudens. 
Page 28. 
1. A portion of the chamber of habitation, showing the numerous regular annulations of the tube 
and the longitudinal striae of the test. 
Hamilton group 1 Livingston county, N. Y. 
Orthoceras expositum. 
Page 29. 
2. An imperfect individual preserving the greater part of the chambered portion of the tube, and 
portion of the chamber of habitation. 
Iron ore bed of the Chemung gi-ouji. Canton, Bradford county, Pennsylvania. 
Orthoceras consortale. 
Page 29. 
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 ti-aces of the surface markings are pre¬ 
served on different parts of the tube. 
4. Id. A natui-al longitudinal section of five aii--chambers, showing the moniliform siphuncle and 
the rays on the upjier bead at its contract with the sejitnm. 
5. Id. A septum showing the position 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. 
6. A longitudinal section of three air-chambers, showing the small passage made by the siphunrile 
through the sejita, and the reflection of the margin indicating a moniliform siphuncle. 
7. A fragment showing the enlargement of the tube, and depth of the air-chambei’S. 
8. The chamber of habitation showing its extent, and a broad constriction near the aperture. 
9. Id. The last septum showing the position of the siphuncle. 
10. A fragment showing the characters of the cj-ganic deposit on the walls of the air-chambers and 
septa. 
Goniatite limestone. Rockford, Indiana. 
Orthoceras Icarus. 
Page 31. 
11. The chamber of habitation with four attached air-chambers, showing the form of the tube and 
the depth of the chambers. 
12. Id. Septum showing the position of the siphuncle, and the circular transverse section of the tube. 
13. Longitudinal section of a chambered fragment showing the passage for the siphuncle through the 
sej)ta. ' 
14. An enlargement to two diametei's of the internal 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. 
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. 4 
Goniatite limestone. Rockford, Indiana. 
