TAB. VI. 



Polyptychodon interruptus. 



Pig. 



1. Centrum of the atlas vertebra, front view. 



2. Centrum of the axis vertebra, back view. 



3. Anchylosed centrums of the atlas and axis vertebrae, upper view. 



4. Ditto, side view. 



These figures, of the nat. size, are from a specimen in the Woodwardian 

 Museum of the University of Cambridge, discovered in the Upper 

 Green-sand formation near that town. 



