40^ G. R. Wieland — Archelon ischyros. 



ral archeg articulated with the centra, and were X-shaped bod- 

 ies with spreading feet which stood well forward on the centra. 

 Subquadrilateral projections extending well forward bear the 

 prezjgapophyses, which are somewhat broken awaj, but seem 

 to have looked forward rather than upward. Immediately over 

 the neural canal the neural spine retreats rather sharply, at the 

 same time taking a keel shape anteriorly, but posteriorly divid- 

 ing and spreading out into alae, which form a distinct deep pit 

 and bear on their under surfaces the postzygapophyses. Pos- 

 teriorly, there is a groove connecting this cup with the neural 

 arch. Anteriorly, the neural spine does not fork as distinctly 

 above as in the very similar vertebrae of Protostega gigas Cope."^ 

 The centra are very heavy and strong bodies, and indicate 

 a neck of enormous strength. They are procoelous, and flat 

 in front, except for the articulating concavity. The anterior 

 upper half rises collar-like on either side of the neural canal, 

 forming an upward and forward-looking articular surface, on 

 which rests the base of the neural arch. The neural canal is 

 scooped out very deeply, and as there is a somewhat similar 

 longitudinal cavity on the nether side, the vertical distance 

 through the centrum is considerably lessened. There are 

 also two similar cavities beneath on the sides, with a heavy 

 ridge, with convex edge, between these and the ventral cavity. 

 Leading from the two lateral concavities around to the neural 

 concavity is a very distinct groove, getting shallower just as it 

 reaches the upper face. 



Measu7'ements of 3rd or Jfth Cervical Vertebra. 



The centrum. Meters. 



Length .._ _ -095 



Width _ -140 



Tx- ^ r 1. • ♦.. ! vertical -065 



Diameter of anterior concavity | horizontal -08 



-p.. , p ^ . ., S vertical '08 



Diameter of posterior convexity | ,^^^^^^^^^^ .^q 



Depth between cup of neural canal and nether 



groove _. -_- '06 



The articulating neural arch. 



Total length '122 



Basal width (total) '11 



Width between the bases _ '045 



Width at top . _ -075 



Distance from base to summit of neural canal. -065 

 Total vertical depth of neural canal '08 



* Cretaceous Vertebrata of the West, Plate XT, fig. 5 a, &, c, d. 



