CHELONIA. 37 



is correspondingly encroached upon, as it were, and narrowed, its broadest part being 

 nearer the anterior end, at the angle between its two straight lateral borders, from 

 which angle the impression extends outwards that divides the occipital from the supra- 

 orbital scute. The frontal scute (/;•) is small and narrow, and the large supraoi-bital 

 scutes meet in front of it at the middle line. They appear to be divided from the 

 orbits by the encroachment of palpebral scutes (/;/) upon the supraorbitary border. 

 There appears to have been an interoccipital scute in the Chel. jjlanimentum, as in the 

 Chel. lon^icejjs and Chel. convexa. 



Amongst existing Chelones the interoccipital scute is constant only in the Cliel. 

 caouanna — the loggerhead of Catesby and Brown ; but the sincipital scute in this 

 species is vastly larger in proportion than in any of the fossils above described ; and it 

 is further distinguished by the peculiar division of the supraorbital and parietal scutes. 



In the hawks-bill turtle {Chel. imhricata), the supracranial scutes leave as well- 

 marked indentations upon the bones of the cranium as are seen in most of the fossil 

 turtles, but the supraorbital scute is proportionably larger than in any of these, and 

 the proportions and forms of all the other scutes are different. There are, also, two 

 nasal scutes divided by a transverse groove from the frontonasals, which groove I 

 have not yet met with in the corresponding part of any of the fossil Chelonian crania. 



The skull of the Chelone cimeiceps, here described, is from the London clay of 

 Sheppy. 



Chelone subcarinata. Bell. Plate 10. 



The resemblance of this species to Chelone subcristata (p. 24, PL 15) is so con- 

 siderable, that it has not been without some hesitation that I have ventui'ed to describe 

 it as distinct. There are, however, certain characters by which it may be distinguished, 

 and those of sufficient importance to be considered as specific. On comparing it with 

 recent species, and even with most of the fossil ones from the same locality, there is a 

 remarkable evenness in the arch of the carapace, which, with the exception of a slight 

 carina on some of the posterior neural plates, to be hereafter mentioned, forms nearly 

 a perfect arc of a circle, from the extremity of the costal plate of the one side to that 

 of the other, without that flattening of the side which is seen in most other species. 



The nuchal plate (PI. 10, fig. 1, ch) has the posterior margin arched, and there 

 is a short median process which goes to join the first neural plate (*l), in which respect 

 it agrees with Chel. lo)i(/ice2)s and with Chel. subcristata. This process is emarginate, to 

 receive a slight triangular projection of the anterior margin of that plate. The first neural 

 plate {s\) forms a parallelogram, the sides not being interrupted by any costal suture ; 

 the posterior suture of the first costal plate (jo/l) extending to the second neural plate 

 (6'2). In this circumstance it differs from Chel. subcristata, lofipcejjs, and convexa, and 

 agrees with Chel. breviceps. This, however, may possibly be a variable character here, as 



