ON BRITISH FOSSIL REPTILES. IGl 



The normal or rounded portion of the rib begins to project from the under 

 surface of the expanded plate at two inches distance from the head of the rib ; 

 but the superincumbent expanded portions and their sutures are continued as 

 far as the marginal plates ; as in other full-grown Emydes. 



Emys testudiniformis, nob. 

 Emys de Sheppey, Cuv. ? 



Most of the Chelonites from the Eocene clay of Sheppey belong to the ma- 

 rine family* of the order, from which the present species differs in the depth 

 of the bony cuirass, the convexity of the carapace, the concavity of the plas- 

 tron, and the extent of ossification of both these parts. The more immediate 

 affinities of the present fossil are elucidated by the comparison of the points 

 of structure which it displays with the anatomical characters of the carapace 

 of the Emys and Testudo. 



The specimen, on which the species Emys testudiniformis is founded, in- 

 cludes a large proportion of the first, second, third, fourth, fifth and sixth, 

 with a fragment of the seventh expanded vertebral ribs of the left side ; a 

 small proportion of the second, third, fourth, fifth and sixth vertebral plates ; 

 the hyo- and hyposternals, and part of the entosternal bones of the plastron. 



The first rib is 1 inch 10 lines, in greatest breadth ; 1 inch 5 lines broad 

 at its junction with the vertebral plates, and four-fifths of the vertebral mar- 

 gin is articulated with the second vertebral plate ; one-fifth part, divided by 

 an angle from the preceding, joins a corresponding side of the lateral angle 

 of the third vertebral plate ; in this structure it resembles both the genus 

 Testudx) and some species of Emys. 



The third, fourth, fifth and sixth vertebral plates are of equal breadth as 

 in Emydes ; not alternately broad and narrow as in the Testudines : they are 

 likewise of uniform figure, as in most Emydes ; not variable, as in Testudines : 

 the vertebral plates also resemble those of the existing Emydes, and particu- 

 larly of the Box-terrapin (^Cistudo) in form. The lateral margin of each is 

 bounded by two'lines, meeting at an open angle, the anterior line is only one- 

 fourth part the length of the posterior one ; and this resemblance may be stated 

 with confidence, since the portion of the entosternal piece preserved in the 

 plastron determines the anterior part of the fossil. 



The ribs preserved in the present Chelonite differ from the corresponding 

 ones of the Tortoises and resemble those of the Emydes in their regular 

 breadth, and the uniform figure of the extremities articulated with the ver- 

 tebral pieces ; the anterior line of the angular extremity is nearly three times 

 as long as the posterior one. 



Further evidence of the relation of the present Chelonite to the freshwater 

 family is given by the impressions of the epidermal scutes : those covering 

 the vertebral plates {scuta vertebralia) agree with those of most Emydians 

 in the very sligiit production of the angle at the middle of their lateral mar- 

 gins, which is bounded by a line running parallel with the axis of the cara- 

 pace, except wliere it bends out to form that small angle. 



The middle part of each side of the plastron, in the Emys testudiniformis, 

 is joined to the carapace by a strong and uninterrupted bony wall, continued 

 from a large proportion of the hyo- and hyposternal bones upwards to the mar- 

 ginal costal pieces. The median margin of the hyo- and hyposternals are ar- 

 ticulated together by a linear suture, traversing the median line of the plas- 

 tron, and only broken by a slight angle formed by the right hyposternal, whicli 

 is a little larger than the left. A similar inequality is not unusual in both Tor- 

 toises and Emydes. The transverse suture is, of course, broken by the same 



* See Proceedings of the Geological Society, Dec. 1, 184L 

 IS'il. M 



