CRETACEOUS CHELONIA. 161 



cylindrical at its humeral half, and gently expanded to a breadth of 3 lines at its sternal 

 end. The proportion which this bone presents of one fourth the length of the 

 carapace is only paralleled in the existing Chelones; it is much shorter in the Eimjdes. 



The hyosternal and hyposternal bones resemble rather those of the Turtles than of 

 the young Emydes ; certainly no Emys, with a carapace 5 inches in length, presents 

 such forms as these bones exhibit in the present fossil ; several rays or pointed spines 

 of bone are developed from the anterior half of the median margin of the hyosternal 

 piece, as in Chelone careffa ; the rest of the margin continues to form the circumference 

 of the large central aperture of the sternum. The hyposternal sends similar rays from 

 the posterior half of its outer margin, leaving the anterior half to join, probably the 

 same proportion of the outer margin of the hyosternal, so as to form a deep, lateral, 

 angular notch of the sternum. The length of the hyposternal is 1 inch 2 lines. The 

 epi-j ento-, and xiphi-sternal bones are not preserved. 



From the preceding description, it must be obvious, as has been already observed, 

 that the present Chelonite of the chalk can only be supposed to belong to the genus 

 Emi/s, on the supposition that it is a very young specimen of some unusually large 

 species ; but against this supposition, the pointed form of the hind end of the carapace, 

 the regularity of the size of the marginal plates, the non-development of the lower 

 margin of any of these plates for a junction with the plastron, the long and slender 

 coracoid, the narrow elongate form of the vertebral plates, and the broad vertebral 

 scutes, collectively and separately militate. Whilst in all these modifications, the Turtle 

 from the Chalk so closely corresponds with the true Chelones, that I cannot hesitate to 

 refer it to the marine family of the order. 



From the breadth of the xiphisternals in the remains of this species first described 

 by me, I was induced to suppose that a new subgenus {Cimoclielys) of marine Turtles 

 was thereby indicated, having a closer affinity to the Emydes than the typical species ; 

 and the same affinity seems to be shown by the more regular elliptical form of the 

 carapace of Mr. Bensted's beautiful specimen. The structure of the cranium, when 

 this desirable part of the skeleton is discovered, may confirm the propriety of the sub- 

 generic distinction ; but the numerous decided marks in other parts of closer affinity 

 to Chelone leave no alternative than to regard the fossil species of the chalk as a 

 member of that genus. 



It differs from all known species, especially the sub-carinated species of Sheppey 

 {Chelone subcarinata and Chelone subcristata), in the form of the carapace, which is more 

 truly elliptical than in any other species with which I am acquainted. 



A second specimen of Chelone Benstedl, of the same size with that above described, 

 also obtained from the lower chalk at Burham, in Kent, and now in the fine collection 

 of J. S. Bowerbank, Esq., F.R.S., gives a better view of the upper surface of the 

 carapace, but the marginal plates have been dislocated and pressed inwards beneath 

 the narrow pointed ends of the ribs. All the neural plates are narrow and carinate 



