1878. ] Saurians of the Dakota Beds of Colorado. 75 
the centra of dorsal vertebra are hollow, including two large cham- 
bers which are separated by a longitudinal median wall, and 
communicate with the cavity ofthe body by a foramen on each side. 
This is well exhibited by a centrum shown in fig. 6, from which 
the anterior wall has been removed, and the mineral contents of the 
chambers extracted. The communication of the latter with the ab- 
dominal cavity is seen on the left side, while the foramen of the right 
side (of the figure) is concealed by its anterior border, which 
remains. 
Fig. 5—A median dorsal vertebra seen from behind, showing the hyposphen. Fig, 
entrum of a dorsal vertebra without anterior wall, ig. 7—Caudal vertebra 
shown in fig. 4, from the right side. Fig. 8—A more posterior caudal, end view of 
the centrum, 
They are also remarkable for the enormous elevation of the 
superior arches, and diapophyses, the result of which is to give the 
ribs an unusually elevated basis, and the cavity of the body 
__ imuch space above the vertebral axis on each side. On the other 
