Chelonia. 



41 



Fig. 54. — a, Frontal, and b, Palatal aspects of the cranium of a young individual of 

 Argillochebjs cuneiceps (Owen), from the London Clay of Sheppey. 'puix, premaxilla ; 

 mx, maxiUa; pt, pterygoid; €^)^ ectopterygoid process of the pterygoid; bo, basi- 

 occipital; a, occipital shield; 6, paraoccipital shield ; c, interparietal shield; d, 

 fiontal shield. J nat. size. 



Fig. 55. — The imperfect carapace of Plcsiocheli/s valdensis (Lydekker) ; Wealden, Isle of 

 Wight (i nat. size). ;ii(, nuchal bone ; '/il-;i7, neural bones; cl-c7, costal bones. 



Teetiaet and Secondary Chelonia. 



