8 FOSSIL REPTILIA OF THE 



above. They are a little broader in front than behind. The slight angular production 

 of the middle of the outer border of the posterior marginal plates is somewhat better 

 marked than in the preceding specimen, and it gives a serrated character to that part 

 of the circumference of the carapace which is formed by those marginal plates. 



An upper view of Mr. Bowerbank's specimen is given in T. Ill, fig. 1 ; a side 

 view in fig. 2 ; an oblique front view, showing some of the anterior marginal plates 

 in fig. 3 ; and an outline of the transverse vertical section of the Turtle in fig. 4 : 

 all of the natural size. 



Chelone pulchriceps, Oioen. T. VII^, figs. 1, 2, 3. 



Keport on British Fossil Reptiles, Trans. British Association, 1841, p. 172. 



With the exception of a few more or less mutilated mandibles, no parts of the 

 skull of a Chelonian reptile have been, hitherto, discovered in the chalk itself, either 

 at Burham or elsewhere in England ; but I have had the opportunity, through the 

 kindness of the Rev. Thomas Image, M.A., of Whepstead, of examining and com- 

 paring the fossil cranium of a small turtle from the green-sand which underlies the 

 chalk. The specimen was discovered near Barnwell, in Cambridgeshire. The general 

 form of the skull is elongate and depressed ; and it is chiefly remarkable for having 

 the nasal bones (15) marked off by a suture from the pre-frontals (14), being a return 

 to the typical characters of the vertebrated cranium, which I have also noticed in 

 the skull of a larger turtle, from the Portland Stone, where, however, the course of 

 the suture is different. 



The characters of the genus Chelone are clearly expressed in the skull of the 

 Chelone pidchricej^s, by the extensive roof of bone over-arching the temporal fossae, 

 and by as large a proportion of this roof being formed by the post-frontals (12) as in 

 existing Chelones. The orbits are also large, and their superior interspace is broad. 



The median or true frontals (11) form a small proportion of the upper border of the 

 orbits; the anterior extremities of the median frontals, instead of converging to a 

 point, are extended forwards, between the pre-frontals, in a broader proportion than 

 in the Portland turtle, and are obliquely truncated : it is only in the genus Chelys 

 among existing Chelonians, that the pre-frontals are thus separated from each other ; 

 but in the Chelys, the intervening extremities of the frontals are continued to the 

 upper border of the external nostril. In the present fossil cranium, the median 

 extremities of the pre-frontals are arrested at the distance of four lines from the 

 nasal aperture, which is bounded above by tw^o distinct nasal bones (15) ; these bones are 

 joined by suture to the frontals, to the pre-frontals, and to the superior maxillaries (21) ; 

 the nasal processes of which extend upward, and exclude the pre-frontals from the 

 nasal boundary. The superior maxillaries are traversed obliquely by a large and 



