162 REPORT — 1841. 



inequality ; that portion which runs between the left hj'^o- and hyposternals 

 being two or three lines in advance of the one between the I'ight hyo- and 

 hyposternals. The posterior half of the broad entosternal piece is articulated 

 to a semicircular emargination at the middle of the hyosternals ; so that the 

 whole plastron forms one continuous plate of bone. This is relatively thicker 

 than in existing Emydes, resembling in its strength that of Tortoises ; and it 

 is likewise slightly concave in the middle, which structure is more common in 

 Tortoises than in Emydians, save those in which the sternum is moveable ; in 

 most of the other species the sternum is flat or slightly convex. 



I have shown in my paper on the Turtles of Sheppey *, that the carapace 

 figured by Cuvierf was not sufliiciently perfect to decide, the affinities of the 

 Chelonian to which it belonged ; if the vertebral scutes were less broad and 

 angular than in marine turtles, the vertebral plates — much less variable in 

 their proportions — were, on the other hand, as narrow as in turtles. But with 

 reference to the plastron of the Sheppey Chelonite, figured by Parkinson I, 

 and supposed by Cuvier to belong to an Emys of the same species as the ca- 

 rapace above alluded to, I have been able to determine, by an examination 

 of the original specimen in the museum of Prof. Bell, that it belonged to the 

 marine genus Chelone and to the species lovglceps. In the fossil JEmys in 

 Mr. Bowerbank's collection, the plastron being in great part preserved, esta- 

 blishes its nonconformity with the marine turtles, and manifests a striking 

 diff'erence from Parkinson's fossil plastron. 



The entosternal piece is impressed, as in Tortoises and Emydes, by a me- 

 dian longitudinal furrow; a transverse linear impression traverses the hyoster- 

 nals half an inch behind the suture of the entosternal; the second transverse 

 line is not so near the first as in Tortoises, but bears the same relation to the 

 transverse suture of the plastron as in most Emydes ; it does not pass straight 

 across the plastron, but the right half inclines obliquely inward to a more 

 posterior part of the median suture than is touched by the left half. The 

 third transverse line passes straight across the plastron between the posterior 

 ends of the bony lateral walls, uniting the carapace and plastron. 



In. Lines. 



The breadth of the plastron is 5 10 



The outer posterior extent of the lateral wall is .... .3 9 



The breadth of the entosternum 1 5 



The depth of the whole bony cuirass at the middle line is 4< 



In the convexity of the carapace and relative depth of the osseous box the 

 Sheppey Chelonite slightly surpasses most existing species, resembling in this 

 respect the JEmys ocellata and Cistudo Carolina. The plastron is also slightly 

 concave, as in the male of Cistudo vulgaris : it is, however, entire at the line 

 where the transverse joint of the plastron exists in the Box-tortoises; and the 

 extent and firm ossification of the lateral supporting walls of the carapace for- 

 bid likewise a I'eference of the fossil to those genera. The general characters 

 of the present fossil, more especially the uniformity of size and breadth of the 

 preserved vertebral plates and ribs, prove it to be essentially related to the 

 freshwater or Emydian Tortoises. It exceeded in size, however, almost all 

 known Emydians, and was almost double the dimensions of the Emydian spe- 

 cies ( Cistudo Europea^ now inhabiting central Europe. It appears, like the 

 Cistudines, to have approached the form of the land-tortoises, in the convexity 

 of the carapace, but without possessing that division and hinge of the plastron 

 which peculiarly distinguishes the box-tortoises. In the thickness and strength 



* Geological Proceedings, December 1, 1841. 

 t Ossem. Foss., torn. v. part iv. pi. xv. fig. 12, 

 X Organic Remains, vol. iii. pi. xviii, fig. 2. 



