72 FOSSIL REPTILIA OF THE LONDON CLAY. 



had not become ossified to the extremity of the ribs, and there is consequently a space 

 between the costal and marginal plates, interrupted by the free extremities of the ribs, 

 which just reach to the marginal plates. It is the only specimen of the family which 

 I have seen, amongst the fossil Chelonian remains, in which the whole series of 

 neural plates, with the nuchal and pygal, remain without material injury ; and the 

 plastron is also nearly entire. 



The nuchal plate (fig. 1, ch) would form a triangle with its posterior angle obtuse, 

 but that this angle is truncated for its articulation with the first neural (si). This 

 latter plate is quadrate, a little longer than broad, and rather narrowed forwards. The 

 second (s2) and third {sz) are also quadrate, and nearly equilateral, The fourth (54) is, 

 however, rendered hexagonal by the termination of the costal suture at a short distance 

 from the anterior margin ; it is quite as broad as it is long. The fifth neural plate (55) 

 is of a similar form, but notably longer than it is broad, forming a broad hexagon, with 

 the lateral angles nearer the anterior than the posterior margins. The seventh (s~) is 

 the only one which forms a nearly symmetrical hexagon, broader than it is long, but 

 with the lateral angles equidistant from the anterior to the posterior margins. The 

 eighth and ninth neural plates (s8, 9) are regularly quadrate, the former being broader 

 than it is long, the latter forming a perfect square. It is very remarkable how much 

 more closely the seventh and following neural plates to the tenth are united than any 

 of the anterior ones ; indeed the sutures between the seventh and eighth, and between 

 the eighth and ninth, are with difficulty observable, notwithstanding the youth of 

 the individual. The tenth neural (s\o) and the pygal (p) plates are somewhat injured 

 and bent down abruptly by some violence. 



I have dwelt somewhat in detail upon the direction of these_ plates, as their cha- 

 racters evidently bear upon the near relation of this species to the terrestrial type 

 already alluded to. 



The internal margin of the first costal plate (ph) exactly coincides with the length 

 of the first neural. The second and fourth costal plates (ph, 4) expand towards the 

 margin of the carapace, and the third and fifth {ph, 5) become narrower in the 

 same direction in a similar degree. 



The marginal plates present no important peculiarity in this young specimen. 



With regard to the impressions left by the horny scutes, we find that although 

 they are of the ordinary general form, they are less broad and spreading in proportion 

 to their length, than is ordinarily the case in the Emydidee, and particularly in 

 immature age ; thus offering another character approaching the terrestrial type. 



The plastron (fig. 2) is tolerably perfect, and presents the remarkable expanse 

 which ordinarily characterises the land and fresh-water forms, but especially the former ; 

 and the anterior and posterior openings between the carapace and the plastron, for 

 the exit and play of the extremities, are somewhat contracted, and thus appear 

 scarcely to afford sufficient room for the natatorial habits of an aquatic species. 



