EXPLANATION OF PLATE XXIII. 



Figs. 1-14. Clidastes planifrons, one-half natural size. 

 Fig. 1. Eight neurapophysis of the atlas. 



2. Axis, with odontoid hone, hypapophysis of latter wanting; 2 b, the same, inferior view. 

 Figs. 3-6. Cervical vertebrae in order ; a, free hypapophysis, proximal surface ; b, inferior, c, anterior, d, 



superior, and, e, posterior views of the same. 

 Figs. 7-13. Some of the dorsal vertebrae in order ; 7 b, the (?) first dorsal from below ; c, from in front ; 



and, e, from behind ; 13 b, a posterior dorsal from below ; c, front ; e, posterior extremity. 

 Fig. 14. Basi-occipital and part of sphenoid, from below. 



15. Exoccipital, from above and behind. 

 Figs. 16-18. Sironectes anguliferus, one-half natural size. 

 Fig. 16. ? Third cervical from above, exhibiting zygosphen. 



17. Last cervical, displaying zygantrum; zygosphenal articulation indistinct, through error of 



artist. 



18. Terminal portion of the articular bone from the outside, showing the suture wiili the sur- 



angular. 



