PLATE LXXXIV. 
Orthoceras sebttlatum. 
Page 283. 
See Plates 38, 86. 
Fig. 1. A fragment in which the last air-chambers are destroyed by maceration and compression, and the 
action of iron pyrites. This is a common condition with the specimens in the soft shales. 
Fig. 2. A larger individual in the same condition of preservation as the preceding, retaining the greater 
part of the apical portion. 
Fig. 4. The apical portion of an example, showing the regular increase in the depth of the air-chambers 
from the apex to the larger extremity. 
Fig. 6. A fragment of a small individual, preserving the test with its markings over a portion of the tube. 
Fig. 7. Another individual nearly entire, but somewhat compressed. The exterior test covers the anterior 
air-chambers. 
Fig. 7 -f- id. A portion of the surface enlarged to show the fine, regular, longitudinal striae, and the more 
irregular lines of growth. 
Fig. 8. An individual retaining the test over nearly the entire exterior. 
Fig. 9. An enlargement of the surface of a specimen similar to figs 1, 2, showing the fine, irregular, lamel- 
lose lines of growth. 
Fig. 10. A septum showing the position of the siphuncle. The specimens of this species here represented 
are all from the softer shales of the Hamilton group at Pratt's Falls, Onondaga county, N. Y. 
Orthoceras exile. 
Page 290. 
See Plates 39, 85. 
Fig. 3. The chambered portion of a large iudividual, which has been flattened from compression. Some of 
the septal sutures are oblique from this cause. The apical portion has been macerated and the 
characters obliterated in a manner similar to figs. 5, 6, pi. 87. Hamilton group. Hamburgh, 
Erie county, N. F. 
Orthoceras terstjm. 
Page 2S6. 
Fig. 5. Dorsal view of a fragment. The other side of the specimen shows the ventral carina along the tube. 
Orthoceras Bebryx. 
Page 275. 
See Plates 38, 39, S3. 
Fig. 11! A septum of a small fragment referred with doubt to this species, showing the subcentral position 
of the siphuncle. 
Fig. 12. An outline from another individual, showing the normal, circular, transverse section of the tube. 
York, Livingston county, N. Y. 
Orthoceras constrictum. 
Page 288. 
See Plate 85. 
Fig. 13. A compressed chamber of habitation. The septa marking several air-chambers, composing the 
lower part of the figure, are not represented. The specimen is covered with a branching para¬ 
sitic Bryozoan. 
Fig, 14. The chamber of habitation of an individual showing a constriction near the middle. 
