172 REPORT — 1841. 



principal bones of the hind-extremities or paddles, which are much shorter as 

 compared with the fore-paddles and the body generally, in the marine than in 

 any of the freshwater or land Chelonia. The length of the femur is 1 inch 

 9 lines ; that of the tibia 1 inch 7 lines. The articular extremities are too 

 imperfect to allow of a comparison of the forms of these bones with the cor- 

 responding ones of existing species. 



Since the carapace of the Chelone obovata approaches, in those modifications 

 by which it differs from other turtles, to the Emydian type, it is not impro- 

 bable that the skull of the Chelonian, above described, from the contiguous 

 subjacent stratum of Portland stone, which offers analogous approximations 

 to the Emydian group, may belong to the same species. 



fVealden Chelone, sp. indeterm. — Portions of the carapace and plastron, 

 and bones of the extremities of a large species of marine turtle, some of 

 them indicating individuals with a carapace nearly three feet in length, have 

 been discovered by Dr. Mantell in the Wealden strata of Tilgate Forest, and 

 are figured in his valuable ' Illustrations of the Geology of Sussex.' 



No specific characters are deduced from these fossils, and the nature of the 

 specimens seems not to have allowed the approximation to be carried closer 

 than to the marine genus Chelone. With regard to one of the specimens, 

 (pi. vi. fig. 2.) however, Mr. Clift's authority is quoted for its resemblance 

 with the corresponding part of Chelone itnbricata, and Dr. Mantell acknow- 

 ledges that " as Cuvier had referred the turtles of Melsbroeck to the Emydes, 

 we at first entertained doubts whether our appropriation of this specimen to 

 the Chelonice were correct. Mr. Clift's remark, however, tends to confirm the 

 opinion that it belongs to a marine turtle," loc. cit., p. 62. 



After a careful comparison of the specimens in the Mantellian Collection* in 

 the British Museum, I have come to the conclusion that the Wealden species 

 differs from Chelone imbricata, Ch. carmata, and other known species in as 

 great a degree as do many of the other extinct Chelones, in regard to the 

 greater extent of the ossification of the costal interspaces and of the sternum. 



In the convexity of the under side of the vertebral ribs ; and in the modi- 

 fications of the form of the episternal, hyosternal and hyposternal bones the 

 Wealden species offers the nearest resemblance to the Chelone planimentum 

 of the Harwich Eocene clay. It is to be regretted that this relationship can- 

 not be more decisively tested by a comparison of the skulls, and especially of 

 the lower jaw of the two species : l)ut these parts of the skeleton appear not to 

 have been as yet discovered in the Wealden. 



Chelone pulchriceps, nob. — The cranial anatomy of a fossil turtle from the 

 superincumbent beds of lower greensand differs from that of other known 

 species, but presents the nearest resemblance to that of the turtle from the 

 Portland stone. 



A small cranium of the present species of Chelone, from the greensand 

 near Barnwell, Cambridge, in the museum of the Rev. Thomas Image of 

 Whepstead, in the same county, is depressed, and likewise has the nasal bones 

 marked off by a suture from the anterior frontals, but in a different manner 

 from that in the skull of the Portland turtle. The characters of the genus 

 Chelone are clearly expressed by the extensive roof of bone overarching the 

 temporal fossae, and by as large a proportion of this roof being formed by the 

 post-frontals as in existing Chelones. The orbits are also large, and their 

 superior interspace is broad. 



The median frontals form a small proportion of the upper border of the or- 



* No. 2338, " Sternal plate of a marine turtle," MS. Catalogue of Mantellian Museum, 

 now in the British Museum, is unquestionably the left hyposternal, and part of the lateral 

 wall, supporting the carapace of a Tortoise or Emys. 



