Fig. 10. — Series of septal sections made from one of the latest 

 septa of the Dactvlioceras/y/^r*?^/ in PL II, ff/- ^- X 2. 



[The horizontal lines indicate the position of the datum-plane. The broken 

 lines indicate the positions of the ribs on the original surface. The 

 letters correspond Avith the numbers of fig. 11, p. 44.] 



