PLATE 72. 
Page 
Fig. 1. Orthoceras tenuiannulatum. 845 
1. A fragment, natural size. 
Fig. 2. Orthoceras helderbergi^:. 845 
2. A specimen of this species, showing some remains of septa. 
Fig. 3. Orthoceras perstriatum. 846 
3. A fragment preserving a part of the outer chamber and several of the chambers above, 
from which the shell is partially exfoliated. 
Fig. 4. Orthoceras rudis. 346 
4 a. The fragment, somewhat flattened from pressure. 
4 b. A section showing the subccntral position of the siphuncle. 
Fig. 5. Orthoceras pauciseptum. 346 
5 a. A fragment of this species. The lower chamber is cut longitudinally, to show the place 
of the siphuncle. 
5 b. Transverse section, showing the excentric position of the siphuncle. 
