PLATE LXXXI. 



Orthocekas pkavum. 



Pago 25S. 

 See Plates 35, 36, 112. 



Fig. 1. An individual, preserving the base of the chamber of habitation and eight adjacent cham})er8. The 

 specimen is much flattened and distorted from compression ; the chambers have become par- 

 tially sei)arated along one side, and their normal form much modified. Clarksville, N. T. 



Fig. 2. A septate fragment, showing the regularity in the depth of the chambers and the gradual enlarge- 

 ment of the tul)e. The lower portion has been flattened, producing a longitudinal furrow, as 

 represented in the figure, probably from the infolding and subsequent erosion of the shell. 

 The oi-namentation on the margins of the septa and on the chamber walls is not shown in the 

 figui"e. 



Fig. 3. A email ft-agment of five chamliers, showing the concave and convex chamber walls, as produced by 

 compression. Schoharie, N. T. 



Fig. 4. A longituciinal section of thi-ee of the chambers of the preceding specimen, showing the indentations 

 in the septa made by tne siphuncle. No traces of the siphuncle, in its passage through the 

 chambers, can be observed. The figure does not quite con-ectly represent the depth of the 

 chambers, and is not complete above. 



Fig. 5. Ventral view of two chambers from the upper portion of the specimen figure 2, showing the exten- 

 sion of the areola to the margin of the septa, and its surrounding with concentric strise. 



Fig. 6. The apical portion of an individual, presenting the appearance of a gradual absorption and final 

 truncation of the shell. The siphuncle has become exposed from the process of weathering. 

 Shai-p longitudinal strise, partially represented, but shown over several chambei-s, are prob- 

 ably the remains of the ornamentation or vascular markings on the septa. iSchoJiarie, N. Y. 



Fig. 7. A septum, showing the areola and its strife surrounding the siphuncle and extending to the ventral 

 margin. 



Fig. 8. Another example, similar to the preceding, somewhat enlarged. 



Orthoceras oppletum. 



PageSS48. 

 See Plate 112. 

 Fig. 9. Ventral view of a fi-agment, showing the lamellose strife on the chambers and septa, and the cylin- 

 drical aggregation of the organic deposit around the siphuncle. Schoharie, N. T. 

 Fig. 10. Lateral view of the preceding specimen. The strise are seen to be concentric about a point on one 



of the septa. 

 Fig. 11. A septum of the preceding specimen, showing the size and position of the siphuncle. 

 Fig. 12. A fragment, with the cavities of the chambers nearly filled v«th an organic deposit. Schoharie, N. T. 



Orthoceras luxch. 



Page 244. 

 See Plates 35, 76, 77, 78, 78 B, 112. 

 Fig. 13. A septate fragment, with the exterior walls of the chambers removed, leaving the cylinder of 

 organic deposit surrounding the siphuncle. The septa ai-e closer together, and the furrows on 

 the cylinder are smaller than in the preceding species. 



