1G4 REPORT — 1841. 



The vertebral plates are all smooth and flat ; their dimensions are as fol- 

 lows: — In. Lines. 

 Length of the fourth plate ...... 1 1 1 



Greatest breadtli . . . ' 1 3 



Length of the fifth plate 1 8 



Greatest breadth 1 3 



Length of the sixth plate 1 6 



Greatest breadth 1 3 



Length of the seventh plate 1 1 



Greatest breadth 1 3 



Length of the eighth plate 9 



Greatest breadth 1 



In the circumstance of the vertebral plates in this fossil decreasing in length 

 without losing breadth, as well as in the junction of the seventh pair of ribs, 

 the present fossil resembles the Sheppey carapace from Mr. Crow's collection 

 figured by Cuvier ; which may, therefore, have belonged to the present spe- 

 cies of Platemys. 



Platemys Bullockii, nob. — A very fine plastron of a Platemys from Shep- 

 pey was obtained by the British Museum at the sale of Bullock's collection, 

 which differs from the preceding in the finely punctate character of the ex- 

 ternal surface of the bone, and in the narrower notches between the body of 

 the plastron and the lateral alae or uniting wall. The following are dimen- 

 sions of this specimen : — In. Lines. 



Length 16 6 



Extreme breadth (anterior to lateral wall) 8 



Breadth or transverse extent of lateral wall 2 6 



Antero-posterior extent of lateral wall 5 6 



Antero-posterior extent of carapace anterior to lateral wall . 5 

 Antero-posterior extent of carapace posterior to lateral wall 6 



The anterior contour of the sternum is rounded ; the posterior termination 

 is notched. The lateral wall extends horizontally, almost parallel with the 

 plane of the sternum, and expands to join, by a wavy suture, the marginal 

 plates ; six of these are preserved on each side ; their lower margins form a 

 very open angle. The anterior part of the entosternum is bounded by two 

 nearly straight lines, converging forwards at an angle of 65°, with the apex 

 rounded off; the posterior contour of this bone is semicircular. The length 

 of the entosternal is 2 inches 10 lines ; its breadth 3 inches 7 lines. 



The chief peculiarity of this plastron is the intercalation of a supernume- 

 rary piece of bone between the hyosternal and hyposternal elements, on each 

 side ; so that the plastron is crossed by two transverse sutures, instead of one ; 

 each suture being similarly interrupted in the middle by an angular deflection 

 from the right, half an inch back, to the left side. The extremities of the 

 transverse sutures terminate each at the apex formed by the inner or lower 

 border of the parallel marginal plates. The first or anterior of these sutures 

 is distant from the anterior margin of the plastron 6 inches 5 lines : the second 

 suture is distant from the same margin 8 inches 9 lines : the right half of the 

 suture, which is a few lines in advance of the left, is the part from which 

 these measurements are taken. 



It might be suspected that the transverse impressions of the second or third 

 pairs of sternal scutes had liere been mistaken for a suture ; but due care was 

 observed to avoid this error: the sternal scutes have left obvious impressions, 

 which prove that they were in the same number as in the Platemydians ge- 

 nerally, and quite distinct from the sutures in question. 



