WEALDEN CHELONIANS. 187 



ordinary nine pieces : where the accessory pair of mesosternal pieces is introduced, 

 both the hyo- and hypo-sternals have relatively less antero-posterior extent than 

 the fossil in question shows. 



Platemys, sp. dub. Plate 52, fig. 2. 



A second species of Wealden Platemys is apparently characterised by a some- 

 what broader plastron, and by a greater relative thickness of the bones composing 

 both this and the carapace. Without the latter difference, the proportionally broader 

 plastron might be merely the sexual distinction of the female of the first species. 

 Some difference, in the shape of the axillary notch of the hyosternal further induces 

 me to regard the fragmentary Chelonites in question, of which a hyosternal is 

 figured in Plate 52, as belonging to a second species of Wealden Platemys. 



Platemys Dixoni, Owen. Plate 52, fig. 3. 



A Platemydian specifically distinct fi'om either of the above is more unequi- 

 vocally exemplified by the sternal element represented in figure 3 ; the matrix 

 having been carefully removed from the outer surface of this fossil, the linear 

 impressions which have divided the humeral from the pectoral scute, and this from 

 the abdominal scute, are clearly shown. The positions of these transverse 

 grooves accord with those in the hyosternal of the Bmydians, having the usual 

 number (nine) of plastral elements : and the hyosternal character of the fossil is 

 further shown by the oblique border cutting off the inner angle of the anterior 

 end, for articulation with the entosternal element, (This end has been figured 

 downwards in the plate.) The axillary groove is narrower than in the above- 

 described species ; and the whole bone seems to have been longer in proportion to 

 its breadth. It is from the Wealden of Tilgate Forest, and formed part of the 

 Collection of the Author of the instructive Work, ' On the Cretaceous and Tertiary 

 Formations of Sussex,' Frederic Dixon, Esq., F.G.S. 



Genus — Chelone. 



Chelone costata, Oicen. Plate 51. 



From the Wealden Clays of Tilgate Forest have been obtained many frag- 

 mentary Chelonites, indicative of species representing two of the actual families of 

 the order, viz. Paludtnosa and Marina ; and such, therefore, as might be expected 



