Chelonia. 



FIG. 50. Frontal aspect of the cranium of 

 Rhinochdys cantabrigiensis (Lydekker) ; 

 from the Greensand, Cambridge. . pmx, 

 premaxilla; mx, maxilla; na, nasal; p.fr, 

 prefrontal ; fr, frontal ; pi. fr, postfrontal ; 

 pa, parietal (the cranium is imperfect 

 posteriorly). 



pnvat 



FIG. 51. Frontal aspect of the cranium of 

 Argillochelys antiqua (Konig) ; from the Lon- 

 don Clay of Sheppey, J-. pmx, premaxilla; 

 mx, maxilla; qj, quadratojugal ; prf, pre- 

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

 parietal. 



FIG. 52. The cai*apace of Nicoria tricatinata. 

 var. sivalensis (Lydekker), nat. size. Pliocene, 

 Siwalik Hills, India. (The dotted lines indicate the 

 bony sutures, the dark lines the horny shields.) 



FIG. 53. The plastron, or ventral shield, of 

 Pleurostcrnum Buliocki (Owen), from the Purbeck 

 beds oi Swanage, Dorset. About nat. size; ig., 

 intergular shield ; ms.p., mesoplastfon ; the rest of 

 the letters and explanation as in Fie:. 49. 



TEETIAEY AND SBCONDAEY CHELONIA. 



