40 CHELONIA. 



R. 20. Slab showing fragments of a comparatively large plastron. 



Gardner Collection. 



R. 28. Slab with fragment of a large costal. Gardner Collection. 



R. 22. Slab showing the dorsal aspect of the femur of a medium- 

 sized turtle. Gardner Collection. 



R. 23. Slab showing the dorsal aspect of a smaller femur. 



Gardner Collection. 



47210. Slab exhibiting the dorsal aspect of a still smaller femur. 



Gardner Collection. 



R. 24. Slab showing the dorsal surface of an imperfect left scapulo- 

 precoracoid. Gardner Collection. 



R. 21. The centrum of a small dorsal vertebra, in matrix. 



Ga rclner Co llectio n . 



R. 28. The centrum of a caudal (?) vertebra, in matrix. 



Gardner Collection. 



Genus ARGILLOCHELYS, Lydekker 1 . 



Skull short and wide, with the orbits and nares directed slightly 

 upwards, a wide interorbital bar, and usually an occipital shield. 

 Palate with low alveolar walls, and a swelling ridge on either side 

 separated by a median groove ; pterygoids short, wide anteriorly, 

 deeply emarginate, with prominent ectopterygoid processes at their 

 antero-exterual angles. Palatal apertures of temporal fossae as 

 wide as long ; posterior nares in anterior half of cranium ; vomer 

 long and joining the elongated premaxillae. Mandibular symphysis 

 of moderate length, convex inferiorly, with the oral surface ridged ; 

 length of postsymphysial portion in some cases less than twice that 

 of the symphysis. 



Shell and the bones of pectoral girdle and limbs apparently of the 

 general type of those of Thalassochelys. The carapace has, however, 

 but four costal shields, and the xiphiplastrals unite extensively in 

 the middle line, while in one case the plastron is much less ossified 

 than in the existing genus. The humerus may also be more con- 

 stricted than in the latter. 



1 Quart. Journ. Geol. Soc. vol. xlv. p. 236 (1889). 



