40 
Chelonia. 
Fig. 50. — Frontal aspect of the cranium of 
Rhinochelys cantabrigiensis (Lydekker); 
from the Greensand, Cambridge. pmx, 
premaxilla; mx, maxilla; na, nasal; p fr, 
prefrontal ; /r, frontal ; pi. fr , postfrontal ; 
pa, parietal (the cranium is imperfect 
posteriorly). 
Fig. 51. — Frontal aspect of the cranium of 
A rgillochelys antiqua (Konig) ; from the Lon- 
don Clay of Sheppey, }. pmx, piemaxilla; 
max, maxilla ; qj, quadratojugal ; prf, pre- 
frontal ; fr, frontal ; ptf, postfrontal ; par, 
parietal. 
Fig. 53.— The plastron, or ventral shield, o: 
PI eurosternum Bullocki (Owen), from the Purbecl- 
beds of Swanage, Dorset. About a nat. size; ig. 
intergular shield ; the rest of the letters and ex' 
planation as in Fig. 49. 
Fig. 52. — The carapace of Nicoiia tricaiinata. 
var. sivalensis (Lydekker), £ nat. size. Pliocene, 
Siwalik Hills, India. (The dotted lines indicate the 
bony sutures, the dark lines the horny shields.) 
Tektiaby and Secondaby Ciielonia 
