PLATE CXIU— Continued. 

 Orthoceras textum. 



Page 285. 

 Fig. 14. An indi^-idual showing the form of the shell and the character of the surface-markings, which are 

 preserved over the entire exterior of the tube. Limestone of the age of the Hamilton proup. 

 .Fiiils of the Ohio, near Louisville, Ky. 



Orthoceras tenere. 



Page 285. 

 Fig. 15. An indi\'idual preserving several air-chambers near the apex, and showing the form of the tube. 

 This specimen and the preceding erf 0. textum' have become silicified, and the internal charac- 

 tei-s of the septa and siphuncle are obliterated. From limestone of the age of the Hamilton 

 group. Fblls of the Ohio, near Loiiismlie, Ky. 



Orthoceras pustis. 

 Page 381. 

 See Plate 83. 

 Fig. 16. The chamber of habitation entii-e, with several attached air-chambers. The septate portion is 

 covered with the test and shows the surface charactere. The chamber of habitation i-etains 

 fragments of the test and shows the internal mould, which is marked by a decided constric- 

 tion of the tube near the aperture, and a more gentle constriction near the base of the chamber. 

 The ai>erture is entii-e, and a small fragment of the test presents its natural acute margin. 

 Goniatite limestone. Schoharie, N. Y. 

 V\g. 17. A septum of the preceding, showing the central position of the siphuncle. 



Orthoceras Marcellbnse. 



Page 278. '-^ 0'*BVi-^ 



See Plates 38. 83, 

 . /, '. - / 

 Fig. 18. A fragment showing the internal mould of the air-chambers and the characters of the organic 



deposit. The larger extremity preserves three longitudinal carinae, of which the central one is 



stronger, and marks the ventral side of the tube. Proceeding in the direction of the apex, the 



organic deposit is firat exhibited as small, iiTegular masses of calcareous matter, arranged 



somewhat symmetrically in regard to the venti-al line. It increases in amount and complexity, 



until, at the smaller extremity, the cavities of the air-chambei-s are nearly filled with the 



dep )8it. Goniatite limestone. Manlius, iV. Y. 



Orthoceras cochleatum. 



Page 308. 

 Fig. 19. An individual nearly entire, showing the form of the tube and the curvature and obliquity of the 

 septal sutures. The chamber of habitation shows a slight constriction of the tube near the 

 aperture, with a contraction at the aperture, and preserves traces of transverse lamellose 

 surface-markings. Upper Chemung group. Warren, Pa. 



Orthoceras bipartitum. 



Page 313. 

 Fig. 20. A small fragment preserving a portion of the gr..nd chamber, with ten attached air-chambers, 

 showing the prominent annulations on the chamber of habitation, and their absence over the 

 septate portion. The intei-nal mould preserves traces of sharp longitudinal striae and trans- 

 veree lines of growth. 



