﻿551 



There seems to have been no close bending of this whorl sufficient 

 to cause the formation of a dorsal furrow in this shell. 



The ananeanic volution given in section, Fig. 16, is too rounded, 

 the lateral zones in this specimen are quite flat and convergent as 

 in adults, and the abdomen is also flattened. The zone of contact 

 is marked by a shaded space in Fig. 16 and is deep and well 

 marked off from the dorsal furrow above in the same figure. 



CENOCERAS L1NEATUM. 



Nautilus lineatus, Sow. {Min. Conch., PI. 141). 

 Nautilus lineatus, D'Orb. {Terr. Jurass., PI. xxxi). 



Loc, Bayeux, Inf. Oolite. 



PI. xi, Figs. 22-27 an d 28-31. 



The ananepionic and metanepionic substages and part of the 

 paranepionic are shown in Figs. 24-27, and also the cicatrix and 

 general -form and shell ornaments, which last are continued in the 

 adults of several species of this genus. 



The umbilical perforation is small and comma-like, contact tak- 

 ing place on the dorsum of the ananepionic volution. A well- 

 developed dorsal furrow is present in the paranepionic but not in 

 the metanepionic, as shown in Figs. 26, 22 and 23. There are 

 annular lobes in the nepionic stage, but these disappear in the para- 

 neanic substage. 



Figs. 28-31 are so similar to the early stage of this species that I 

 have referred them to it, although this was identified by Quenstedt 

 as Nautilus aratus, Schlot. 



Cenoceras aratum. 

 Nautilus aratus, wSchlot. 



Loc, Suabia, Middle Lias. 



PI. xi, Figs. 32-35. 



The specimen shown in Figs. 32-35 was figured first in my Em- 

 bryology of Fossil Ccphalopods, is one of Saemann's originals and 

 although quite perfect in some respects has no shell. 



It is a cast in iron of the interior and shows the characteristics 

 figured very distinctly. The early beginning of the annular lobe 

 in the third suture and that of the dorsal furrow in the metanepi- 

 onic between the third and fourth sutures is very interesting in view 

 of the fact that this shell had a comparatively large umbilical per- 



