Geological Society. 233 



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 7th 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 ; 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 

 which they are articulated, the present fossil resembles the Chel. 

 longiceps. 



The author knows of no recent example, however, of the Chelone 

 that offers such varieties in the form of its epidermal scutes as would 

 warrant the present Chelonite being considered a variety merely 

 of the Chel. longiceps ; and he therefore indicates the distinct species 

 which it seems to represent, by its main distinctive character, under 

 the name of Chelone latiscutata. 



4. Chelone concexa. — The fourth species of Chelone, indicated by 

 a nearly complete cuirass, from Sheppey, holds a somewhat inter- 

 mediate position between the C. breviceps and C. longiceps ; the ca- 

 rapace being narrower and more convex than that of C. coniceps ; 

 broader, and with a concavity arising from a more regular curvature 

 than in C. breviceps. The expanded parts of the ribs have an inter- 

 mediate length with those of the two Chelones with which this spe- 

 cimen is compared, and therefore is a difference independent of age. 



The distinction of C. convexa is still more strikingly established in 

 the plastron, which in its defective ossification more nearly resembles 

 that of the existing species of Chelone. All the bones, especially 

 the xiphisternals, are more convex on their outer surface than in other 

 turtles, recent or fossil. The internal rays of the hyosternals arc 



