WEALDEN CLAYS AND PURBECK LIMESTONES. 11 



Figure 4, Tab. IX, gives a view of the inner surface of the left hyposternal, half 

 the natural size of, probably, the same species of Chelone. It is imbedded in a slab 

 of Wealden stone. 



As compared with existing Turtles, the ossification of the plastron is more advanced 

 or more extensive, the rays of bone from the outer and inner free borders of the 

 hyposternal being shorter and their interspaces more filled up. A nearer approach is 

 thus made in this Wealden species, as in some of the Eocene Turtles, to what may be 

 regarded as the more general type of the Chelonian carapace. 



Platemys Mantelli. Owen. Tab. IX, fig. 1. 



Report on British Fossil Reptilia, 1841, p. 167. 

 Emys de Sussex, Cuvier. Ossemens Fossiles, 4to, torn, v, part ii, 1824, p. 232. 

 Emys Mantelli, J. E. Gray. 



Amongst the Chelonian Fossils obtained by Dr. Mantell from the Wealden strata of 

 the Tilgate Forest, in Sussex, were certain specimens, the resemblance of which to the 

 flat species of Emydian, or terrapene, discovered by M. Hugi in the Jura limestone at 

 Soleure, has been pointed out by Cuvier, (loc. cit.) Both the Jura species and the 

 Wealden Chelonites in question are referable to the ' pleuroderal' section of the great 

 tribe Paludinosa, as arranged by Messrs. Dumeril and Bibron -^ and, in that section, to 

 the genus Platemys, but so much of the skeleton has not, as yet, been discovered, as to 

 afford a ground for a good specific character of the so-called Emys Mantelli. 



The most intelligible fragment in the British Museum, is that element of the 

 plastron — the hyosternal ; which is figured in Tab. IX, fig. 1. The proportions of 

 this bone indicate that the plastron of the Platemys Mantelli consisted of the 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. Table IX, fig. IL 



A second species of Wealden Platemys is apparently characterised by a somewhat 

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

 and the carapace. Without the latter diff"erence, 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 

 Tab. IX, fig. II, as belonging to a second species of Wealden Platemys. 



1 Erpetologie, 8vo, 1835, torn, ii, pp. 172, 372. 



