PLATE LXXX. 



Orthoceras collatum. 



I'lige 252. 



T\g. 1. A sectate fragrment, showing' a very cylindrical tube and a slight distortion from pressure. The 

 Pt'pta are not all i-epresentetl, bcinjf somewhat obscure, giving the appearance of great irregu- 

 larity in the depth of the chambers. ISclioliarie, 2V. Y. 



Fig. 3. The anterior jx>rtion of an individual, i-etaining the chamber of habitation and five adjacent cham- 

 bei-s. A marked and peculiar constriction is .shown on the upjier portion of the chamber of 

 habitation. 



Fig. 4. A septum of the pi-eceding specimen, showing the size and position of the siphuncle, and the amount 

 of flattening of the tube from compression. 



Orthoceras tetricum. 



See Plate 78 B. 



Fig. 2. A septate fragment, showing the smooth and flat chamber walls. Clarkumlle, N. Y. 



Fig. 5. A fragment, very much broken, but retaining its normal form and convexity. A poi'tion of the test 

 remaining on the s|)eciu)en is not represented in tlie figure. 



Fig. 6. Septum of the precetiing specimen, showing the position of the siphuncle and the circular transverse 

 section of the tube. 



Fig. S. A longitudinal section of a small septate fragment, shfiwing the depth of the chambers and the con- 

 cavity of the septa. No traces of the siphuncle can be observed. Schoharie, N. Y. 



Fig. 9. A longitudinal section of a larger individual, with a pcirtiou of the chamber of habitation. The 

 inteiior of the tube contains several specimens of Stieptelasma and othei' fossils, shown in section. 

 Schoharie, iV. i'. 



Orthoceras Thoas. • 



I'age-261. 



See Plates 41, 78 B, 79, 112. 



Fig. 7. A £e|)tum of specimen fig. 4, pi. 41, showing the position of the siphuncle, and the indentation made 



in its passage through the sejjtum. Schoharie, N. Y. 

 Fig. 10. A longitudinal section of an indivi<lual, 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 thi'ough the septa. Ti-aces of a nummuloid 

 siphuncle, shown in the specimen, are not represented. 



