186 BRITISH FOSSIL REPTILES. 



great relative size, more especially the superior breadth, of the three succeeding 

 vertebral scutes (y 2, v 3, v 4). The boundary lines, indicating the forms and 

 disposition of the horny scutes, are proportionally larger and deeper than in the 

 other species of Plcuro>ifernon which have come under my observation. 



The sutures uniting together the different elements of the carapace are more 

 dentated or wavy, more especially the suture uniting the nuchal plate with the 

 first neural plate and first pair of costal j^lates. The neural plates, from the first 

 to the seventh inclusive, are similar in form, six-sided, with the antero-lateral 

 sides the shortest; the eighth neural plate is the smallest, is four-sided, and 

 broadest behind ; the ninth and tenth neural plates are remarkable for their great 

 breadth . 



The transverse extent or length of the costal plates is considerable, in 

 accordance with the great breadth of the carapace : the eighth costal plate, in this 

 respect, differs considerably from its homologue in the other species of Pleuro- 

 sternon. The second marginal scute is not produced backwards between the first 

 vertebral and first costal scute, but, like the first and third marginal scutes, has 

 its antero-posterior diameter much less than the diameter in the direction of the 

 periphery of the carapace. The first (c 1) and fourth {e 4) costal scutes differ 

 considerably in their forms and proportions from those in Plates 53, 55, and 57. 



The outer surface of the osseous parts of the carapace of Pleurosternon 

 latiscutatum is minutely punctated and rugose, except near the sutural borders of 

 the several pieces, where it is impressed by rather coarse parallel striae, directed 

 at right angles to those borders. 



Genus — Platemts. 



Platemts Mantelli, Owen. Plate 52, fig. 1. 



Amongst the Chelonian Fossils from the "Wealden strata of the Tilgate Forest, 

 in Sussex, are certain specimens which resemble the flat species of Emydian, or 

 terrapene, discovered by M. Hugi, in the Jura limestone at Soleure. Both the 

 Jura species and the Wealden Chelonites in question are referable to the ' pleuro- 

 deral' section of the great tribe Faludinosa, as arranged by Messrs. Dumeril and 

 Bibron ;' and, in that section, to the genus Platemys. 



The most intelligible fi'agment in the British Museum, is that element of the 

 plastron — the hyosternal, which is figured in the above Plate. The proportions 

 of this bone indicate that the plastron of the Platemys Mantelli consisted of the 



» ' Erpetologie,' 8vo, 1S35, torn, ii, pp. 17L', 372. 



