PLATE XC. 
Orthoceras Demus, 
Page 311. 
Fig. 1. A chambered fragment showing the depth of the air-chambers. The specimen does not preserve 
any additional characters, and is referred to the species^ with some hesitation. In the arena¬ 
ceous shales, at Philipsburgh, N. Y. 
Fig. 4. A fragment retaining its normal proportions, and showing the characters of the species. Chemung 
group. Cascadilla creelc, Ithaca, N. Y. 
Fig. 5. A small fragment in which the tube has been filled with iron pyrites, and the characters obscured. 
Chemung group. Ithaca, N. Y. 
Orthoceras fulgidum. 
Page 310. 
Fig. 2. An individual retaining the chamber of habitation nearly entire, and eleven of the attached air- 
chambers, showing the enlargement of the tube and the distance between the septa. Several 
fragments of the test are adheiing to the internal mould of the tube. Chemung group. Casca¬ 
dilla creek, Ithaca, N. Y. 
Fig. 3. A portion of a larger individual somewhat compressed, giving curvature and obliquity to the septal 
sutures. Chemung group. Ithaca, N. Y. 
Orthoceras Leander. 
Page 309. 
Fig. 6. A fragment somewhat compressed at the lower extremity, and showing the siphuncle as exposed 
from weathering. Chemung group. South of Ithaca, N. Y. 
Fig. 7. A chamber of habitation and ten attached air-chambers. 
Fig. 8. An individual nearly entire, showing the rapid enlargement of the tube and the characters of the 
chamber of habitation, with the slight expansion and constriction of the tube at the aperture. 
Upper Chemung sandstone. Warren, Pennsylvania. 
Orthoceras palmatum. 
Page 312. 
Fig. 9. Lateral view of a fragment showing the depth of the air-chambers and enlargement of the tube. 
The ventral side of the specimen shows a longitudinal carina along the cast of the walls of the 
air-chambers. 
Fig. 10. A septum of the preceding, showing the size and position of the siphuncle with the raised areola 
around its insertion, and the palmate ornamentation extending to the ventral side of the tube. 
Chemung group. Southern New York. 
Cyrtoceras? Hector. 
Page 364. 
Fig. 11. A fragment preserving the greater portion of the chamber of habitation, with several attached 
shallow air-chambers, showing a slight contraction of the tube at the aperture. Traces of fine 
striae of growth shown on the specimen are not represented. Chemung group. Warren, Penua. 
Fig. 12. Another fragment showing deeper air-chambers. Chemung group. Near Olean, N. F. 
Fig. 13 id. An opposite view, showing the curvature and obliquity of the suture lines. 
Fig. 14 id. A lateral view, showing a greater irregularity in the curvature and direction of the sutures. 
Fig. 15. An outline showing the transverse section of the tube. 
Orthoceras pertextom. 
Page 314. 
Fig. 16. A fragment without evidences of septa, and showing the character and frequency of the annula- 
tions. The surface-markings are shown over the entire surface of the tube. Chemung group. 
Ithaca, N. Y. 
Fig. 17. An enlargement of a portion of the surface of the preceding, showing the crenulated character of 
the striffi. 
