EXPLANATION OF PLATE XVIII. 



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



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

 side view, beginning with the axis. 



2. The axis, from below. 



3. Thiid cervical ; a, from below ; b, from behind ; o, from in front. 



4. Fonrth cervical: a, from before; J, from behind ; c, free hypapophysis. 



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



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



7. Part of vertebral column of Platccarpus curtirostris. 



8. The atlas of Platecarpus curlirostris : o, centrum ; 6, the neurapophysis from the front; c, from 



the inside ; d, from the outside. 



