PLATE LXXXIII. 



Orthoceras Marcellense. 



Page 278. 



See Plates 38, 113. 



Tig. 1. Ventral view of a frag-ment showing, on the cast, a long-itudinal convex line on each aide of the 



median carina. , 



Fig. 2. Ventral view of a larger fragment pi-eserving portions of the test, and showing the ventral carina 



along the internal mould of the air-chambei-s. Giiniatite limestone. MavlUis, N. Y. 

 Fig. 8. A longitudinal section showing the position and elements of the siphuncle, and the depth of the air- 



chamliei-s. 

 Fig. 4. A septum, showing the elevated areola ai-ound the siphuncle, and its extension to the ventral side. 

 Fig. 6. Ventral view of the same, showing the elevation of the areola, and the continuation of the areolar 



process over the walls of the air-chamber. These two figures are from the lower extremity of 



specimen figure 2. 

 Fig. 6. A septum showing the elevated areola and radiating vascular markings, extending to the margins. 

 V\g. 7. A septum showing a simple areola without extension to the ventral margin, and surrounded by 



obscure, radiating, vasculai' markings. 

 Fig. 8. A septum nearer the outer chamber, without distinct areolar markings, showing the position of the 



siphuncle. Atanlius, N. Y. 

 Fig. 9. The concave surface of a septum, which has become distorted from compression. 

 Fig. 10. An enlargement of the surface, showing bi-oad, flat, transverse striee, without any evidences of lon- 

 gitudinal markings. 

 Fig. 12. An enlargement similar to the preceding, from another part of the specimen, with sharper strife 



of growth, and strong longitudinal lines. 



Orthoceras fustis. 



Page 281. 

 See Plate 113. 

 Fig. 11. k portion of the surface enlarged, showing the minutely un<lulating strise of growth, and fine longi- 

 tudinal stiiae. Schoharie, A'. Y. 



Orthoceras, sp. undetermined. 



Page SW. 

 Fig. 13. A fragment of undetermined specific relations. The surface of a septum is covered with nnmeroos 

 individuals of a species of Spirorbis. Hamilton group. Ontario, Cavada West. 



Orthoceras Bebrtx. 



Page 275. 

 See Plates 38, 39, 84. 

 Fig. 14. A fragment much compressed and weathered, with the siphuncle exposed, showing its elements. 

 Skaneatd^ Lake, N. Y. 



