68 POSSIL REPTILIA OF THE LONDON CLAY. 



The middle part of each side of the plastron, in the Bviys testudiniformis, is joined 

 to the carapace by a strong and uninterrupted bony wall, continued from a large pro- 

 portion of the hyosternal and hyposternal bones upwards to the marginal costal pieces. 

 The median margin of the hyosternals and hyposternals are articulated together by a 

 linear suture, traversing the median line of the plastron, and only broken by a slight 

 angle formed by the right hyposternal, which is a little larger than the left. A similar 

 inequality is not unusual in both tortoises {Tesiudinida) and terrapenes {Emi/didce). The 

 transverse suture is, of course, broken by the same inequality ; that portion which runs 

 between the left hyosternals and hyposternals being two or three lines in advance of 

 the one between the right hyosternals and hyposternals. The posterior half of the 

 broad entostemal 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 Einydes, resembling in its strength that of tortoises ; 

 and it is likewise slightly concave m 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 Sheppy,* that the carapace figured by 

 Cuvierf was not sufficiently 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 neural 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 Sheppy Chelonite, 

 figured by Parkinson,;}: and supposed by Cuvier to belong to an Emys of the same 

 species as the carapace above alluded to, I have been able to determine, by an exami- 

 nation of the original specimen in the museum of Professor Bell, that ]it belonged to 

 the marine genus Chelone and to the species lonyiceps. In the fossil Emys in Mr. 

 Bowerbank's collection, the plastron being in great part preserved, establishes its 

 nonconformity with the marine turtles, and manifests a striking difference from 

 Parkinson's fossil plastron. 



The entosternal piece is impressed, as in Tortoises and Emydes, by the median 

 longitudinal furrow, dividing the two humeral scutes ; the transverse linear impression 

 dividing the humeral from the pectoral scutes traverses the hyosternals half an inch 

 behind the suture of the entosternal ; the second transverse line, which divides the 

 pectoral from the abdominal scutes, 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, which divides the abdominal from the femoral scutes, passes straight 



* Geological Proceedings, December 1, 1841. 



t Ossemens Fossiles, torn, v, part iv, pi. 15, fig. 12. 



X Organic Remains, vol. iii, pi. 18, fig. 2. 



