40 



Chelonia. 



F-^/t 



F:g. 50. — Frontal aspect of the cranium of 

 Rhinochelys cantahriciiensis (Lydekker) ; 

 from the Greensand, Cambridge. \. pmx, 

 premaxilla ; 7)w, maxilla ; na, nasal; p.fr, 

 prefrontal ; fr, frontal ; pt. fr, postfrontal ; 

 ■pa, parietal (the cranium is imperfect 

 posteriorly). 



pTTLOl 



Fig. 51. — Frontal aspect of the cranium of 

 Argillnchebis ontifjua (Konig) ; from the Lon- 

 don Clay of Sheppey, }. pmx, premaxilla; 

 riix, maxilla ; qj, quadratojugal ; ^;-/, pre- 

 frontal ; fr, frontal ; ptf, postfrontal ; par, 

 parietal. 



Fio. 52. — The carapace of Ificoria tricminata. 

 var. sivalennis (Lydekker), ^ nat. size. Pliocene, 

 Siwalik Hills, India. (The dotted lines indicate the 

 bony sutures, the dark lines the hnrny shields.) 



Fig. 53. — The plastron, or ventral shield, of 

 Pleumsternum BuUockt (Owen), from the Purbeck 

 beds of Swanage, Dorset. About i nat. size; ig., 

 intergular shield ; in.t.p., niesoplastron ; the rest of 

 the letters and explanation as in Fig. 49. 



Tertiary and-Secondaby Chelonia. 



