20 FOSSIL REPTILIA OF THE LONDON CLAY. 



The breadth of the plastron, at the junction of the xiphisternal with the hyposternals, 

 is two inches six lines. 



The posterior part of the cranium is preserved in Mr. Bowerbank's specimen 

 (fig. 1), withdrawn beneath the anterior part of the carapace ; the fracture shows the 

 osseous shield covering the temporal fossae ; and the pterygoids remain, exhibiting 

 the deep groove that runs along their under part. 



It is most satisfactory to have found that the two distinct species of the genus 

 Chelone, determined, in the first instance, by the skulls only, should thus have been 

 confirmed by the subsequent comparison of their bony cuirasses ; and that the specific 

 differences, manifested by the cuirasses, should be proved by good evidence to be 

 characteristic of the two species founded on the skulls. 



Thus the portion of the skull preserved with the carapace first described (Tab. II, 

 figs. 2 and 3), served to identify that fossil with the more perfect skull of the Chelone 

 breviceps (Tab. I), by which the species was first indicated. And, again, the portion of the 

 carapace adhering to the perfect skull of the Chelone longiceps (Tab. IV, fig. 1) equally 

 served to connect with it the nearly complete osseous buckler (Tab. V, fig. 1), which, 

 otherwise, from the very small fragment of the skull remaining attached to it, could 

 only have been assigned conjecturally to the Chel. longiceps ; an approximation which 

 would have been the more hazardous, since the Chelone breviceps and Chelone longiceps 

 are not the only turtles which swam those ancient seas that received the enormous 

 argillaceous deposits of w r hich the Isle of Sheppey forms a part. 



Chelone latiscutata, Owen. Tab. VI. 



Proceedings of the Geological Society of Loudon, December 1, 1841, p. 574. Report 

 on British Fossil Reptiles, Trans. British Association, 1841, p. 179. 



A considerable portion, measuring three inches in length, of the bony cuirass of a 

 young turtle from Sheppey, including the first to the sixth neural plates (T. VI, fig. 1, 

 s\ — 86), with the corresponding pairs of costal plates (ph — ph), and the hyosternal 

 (fig. 2, hs) and hyposternal (ps) elements of the plastron, most resembles that of the 

 Chelone longiceps in the form of the carapace, and especially in the great transverse 

 extent of the above-named parts of the plastron : it differs, however, from the Chel. 

 longiceps, and the other known fossil Chelonites, in the greater relative breadth of the 

 vertebral scutes {v2, vz), which are nearly twice as broad as they are long. 



The central vacuity of the plastron is subcircular ; and, as might be expected, 

 from the apparent nonage of the specimen, is wider than in the Chel. longiceps ; but the 

 toothed processes given off from the inner margin of both hyosternals and hyposternals 

 are small, sub-equal, regular in their direction, and thus resemble those of the Chel. 

 longiceps ; the slender point of the episternal is) is preserved in the interspace between 



