PLATE 72. 



Fig. 1. Orthoceras tenuiannulatum. 845 



1. A fragment, natural size. 



Fig. 2. Orthoceras helderbergi^. 345 



2. A specimen of this species, showing some remains of septa. 



Fig. 3. Orthoceras perstriatum. 346 



3. A fragment preserving a part of the outer cliamber and several of the chambers above, 



from which the shell is partially exfoliated. 



Fig. 4. Orthoceras rudis. 846 



4 a. The fragment, somewhat flattened from pressure. 

 4 6. A section showing the subcentral position of the siphunclc. 



Fig. 5. Orthoceras pauciseptum. 346 



5 o. A fragment of this species. The lower chamber is cut longitudinally,, to show the place 



of the siphuncle. 

 5 6. Transverse section, showing the excentric position of the siphuncle. 



