EXPLANATION OF PLATE XVIII. 



Vertebra of Pythonomorpha of three species, all more or less incomplete ; one-half natural size. 



Fig. 1. Column of Clidastes stenops, including some of the cervical, dorsal, lumbar, and caudal vertebra? ; 

 side view, beginning with the axis. 



2. The axis, from below. 



3. Third cervical : a, from below ; b, from behind ; c, from in front. 



4. Fourth cervical: a, from before; 6, from behind ; c, free hypapophysis. 



5. A dorsal vertebra : a, from above ; b, from below. 



6. Part of vertebral column of PJalecarpus ictericus, from the side ; a dorsal vertebra from above. 



7. Part of vertebral column of Platccarpus curtiroatris. 



8. The atlas of Plalecarpus curtirostris : a, centrum ; b, the uenrapophysis from the front ; c, from 



the inside ; d, from the outside. 



