170 BRITISH FOSSIL REPTILES. 



notched posteriorly, between the two truncate angles. Its length is 1 inch 5 lines ; 

 its breadth 6 lines : there is no appearance of a carina on its upper surface. The 

 second costal plate, pi. 2, is 3 inches 2 lines in length, 1 inch 4 hues in breadth ; 

 it is slightly concave in the axis of the carapace; convex in the direction of 

 its own length or across the carapace. On the right side it is fractured, and its outer 

 end is overlapped by the dislocated fourth marginal plate, m 4, into the upper border 

 of which the free end of the rib, which now projects below it, was implanted. The 

 upper surface of the costal plate is impressed by the triradiate line of union of the 

 second vertebral scute, v 2, with the first, c l, and second, c 2, costal scutes. The 

 third, pi. 3, and fourth, pi. 4, costal plates have their median ends straight with the 

 posterior angles truncate. About seven lines of the free end of the connate rib pro- 

 jects beyond their broad outer ends. Beyond these the carapace is broken through 

 by the pressure of the plastron from below: the upper surfaces of the conjoined 

 hyposternals appear at ps, ps, the dislocated parts of the carapace, which were above 

 them, having been removed. The outer portions of the fifth and sixth costal plates 

 are seen on the right side, terminating the one, j,i. 5, between the seventh and eighth 

 marginal plates, the other, pi. 6, between the eighth and ninth marginal plates. The 

 seventh and eighth, p/. 7, pi. 8, costal plates are preserved on the left side. The median 

 ends of the eighth pair seem almost or quite to have met anterior to the ninth neural 

 plate, s 9, as in the Mnt/s levis* the ninth plate presents a triangular form with the 

 apex turned forwards : the breadth of its base is 1 inch 7 lines, its length is 

 1 inch. The tenth neural plate is a hexagonal one, 1 inch 10 lines in leno-th. 

 It articulates immediately with the pygal plate, py, which is subquadrate, rather 

 broader behind, where it is notched in the middle. Its length is 1 inch 5 lines ; its 

 breadth 1 inch 8 lines. Not any of these neural plates are carinate. 



The left hyosternal {ps] has been displaced, so that its under or outer surface 

 would be in view in the block displaying the upper surface of the carapace, PI. 47, 

 were not the major part of its substance retained in the other half of the block, which 

 therefore shows in part the contour of its upper or inner surface, PL 48, fig. 11, from 

 which, however, the produced outer and anterior angle is broken off, that part 

 remaining attached to the other moiety at ps, PI. 47, where it dips beneath the 

 border of the carapace. It is this produced angle which, bending upwards and for- 

 wards, efi"ects the union between the plastron and carapace at the fore part of the 

 lateral wall, by its insertion into the carapace ; and it affords the chief proof of the 

 Emydian affinities of the Chelonite under consideration. 



Yet in some respects, the hyosternal in the fossil resembles more that of a young than 

 of an old Emydian : its median border is not straight, and the concavity of the hinder 

 half of that border indicates a persistent vacuity in the middle of the bony plastron ; 



* History of Brit. Fos. Reptiles (Tertiary Formations), pi. 3, fig. 1. 



