PLATE LXXX. 
Orthoceras collatum. 
Page 252. 
Fig. 1. A seotate fragment, showing a very cylindrical tube and a slight distortion from pressure. The 
septa are not all represented, being somewhat obscure, giving the appearance of great irregu¬ 
larity in the depth of the chambers. Schoharie, 2V. Y. 
Fig. 3. The anterior portion of an individual, retaining the chamber of habitation and five adjacent cham¬ 
bers. A marked and peculiar constriction is shown on the upper portion of the chamber of 
habitation. 
Fig. 4. A septum of the preceding specimen, showing the size and position of the siphuncle, and the amount 
of flattening of the tube from compression. 
Orthoceras tetricum. 
Page 251. 
See Plate 7S B. 
Fig. 2. A septate fragment, showing the smooth and flat chamber walls. Clarksville, iV". Y. 
Fig. 5. A fragment, very much broken, but retaining its normal form and convexity. A portion of the test 
remaining on the specimen is not represented in the figure. 
Fig-. 6. Septum of the preceding specimen, showing the position of the siphuncle and the circular transverse 
section of the tube. 
Fig. 8. A longitudinal section of a small septate fragment, showing the depth of the chambers and the con¬ 
cavity of the septa. No traces of the siphuncle can be observed. Schoharie, iV. Y. 
Fig. 9. A longitudinal section of a larger individual, with a portion,of the chamber of habitation. The 
interior of the tube contains several specimens of Streptelasma and other fossils, shown in section. 
Schoharie, N. Y. 
Orthoceras Thoas. 
Page 261. 
See Plates 41, 78 B, 79, 112. 
Fig. 7. A septum of specimen fig. 4, pi. 41, showing the position of the siphuncle, and the indentation made 
in its passage through the septum. Schoharie, N. Y. 
Fig. 10. A longitudinal section of an individual, retaining the chamber of habitation and one adjacent 
chamber. 
Fig. 11. A longitudinal section of a small septate fragment, showing the depth of the chambers, and the 
projections made by the siphuncle in its passage through the septa. Traces of a nummuloid 
siphuncle, shown in the specimen, are not represented. 
