374- Geological Society : Prof. Owen's Description 



The xiphisternals are relatively broader than in C. breviceps or in 

 any of the existing species, and are united together by the whole of 

 their median margins. The entosternal piece is flat on its under 

 surface. • 



Each half of the plastron is more regularly convex than in C. My- 

 das. The breadth of the sternum along the median suture, uniting 

 the hyosternals and hyposternals, is five inches ; and the breadth at 

 the junction of the xiphisternals with the hyposternals is two inches. 



The posterior part of the cranium is preserved in this fossil, with- 

 drawn beneath the anterior part of the carapace ; the fracture shows 

 the osseous shield covering the temporal fossae ; and the pterygoids 

 remain, exhibiting the wide and deep groove which runs along their 

 under part. 



It has been most satisfactory, the author says, to find that the two 

 distinct species of the genus Chelone, first determined by the skulls 

 only, should thus have been established by the subsequent observa- 

 tion of their bony cuirasses ; and that the specific differences mani- 

 fested by the cuirasses should be proved by good evidence to be cha- 

 racteristic of the two species founded on the skulls. 



Thus the portion of the skull preserved with the carapace first 

 described, served to identify that fossil with the more perfect skull 

 of the Chelone breviceps, by which the species was first indicated. 

 And, again, the portion of the carapace adhering to the perfect skull 

 of the Chelone longiceps equally served to connect with it the nearly 

 complete osseous buckler, which otherwise, from the very small frag- 

 ment 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 Chel. breviceps and 

 Chel. longiceps are not the only turtles which swarm those ancient 

 seas that received the enormous argillaceous deposits of which the 

 isle of Sheppey forms a part. 



3. Chelone latiscutata. — A considerable portion of the bony cuirass 

 of a young turtle from Sheppey, three inches in length, including 

 the 2nd to the 7 th vertebral plates, with the expanded parts of the 

 first six pairs of ribs, and the hyosternal and hyposternal elements 

 of the carapace, most resembles that of the Chelone coniceps in the 

 form of the carapace, and especially in the great transverse extent of 

 the above-named parts of the sternum j it differs, however, from the 

 Chel. longiceps and from all the other known Chelonites in the great 

 relative breadth of the vertebral scutes, 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 hyo- and hyposternals are small, sub- 

 equal, regular in their direction, and thus resemble those of the 

 Chel. longiceps. 



The length of the expanded part of the third rib is one inch seven 

 lines ; its antero-posterior diameter or breadth, six lines ; in the form 

 of the vertebral extremities of the ribs and of the vertebral plates to 



