of the Remains of Marine Turtles from the London Clay. 31 '5 



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 convexa. — 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 are 

 divided into two groups ; the lower consisting of two short and 

 strong teeth projecting inwards, while the rest extend forwards along 

 the inner side of the episternals. The same character may be ob- 

 served in the corresponding processes of the hyposternals, but the 

 external process is relatively much narrower than in C. breviceps. 

 The following differences are stated to distinguish the sternum of 

 C. convexa from that of C. Mydas. The median margin of the hyo- 

 sternals forms a gentle curve, not an angle : that of the hyposternals 

 is likewise curved, but with a slight notch. The longitudinal ridge 

 on the external surface, and near the median margin of the hyo- and 

 hyposternals, is less marked in the Sheppey fossil ; especially in the 

 hyposternals, which are characterized by a smooth concavity in their 

 middle. 



The suture between the hyo- and hyposternals is nearer to the 

 external transverse radiated process of the hyposternals. The me- 

 dian vacuity of the sternal apparatus is elliptical in the Chel. con- 

 vexa, but square in the Chel. Mydas. 



The characteristic lanceolate form of the episternal bone in the 

 genus Chelone is well seen in the present fossil. 



The true marine character of the present Sheppey Chelonite is 

 likewise satisfactorily shown in the small relative size of the entire 

 femur which is preserved on the left side, attached by the matrix to 

 the left xiphisternal. It presents the usual form, a slight sigmoid 

 flexure, characteristic of the Chelones ; it measures one inch in 

 length. In an Emys of the same size, the femur, besides its greater 

 bend, is 1^ inch in length. 



5 . Chelone subcristata. — The fifth species of Chelone from Sheppey, 

 distinguishable by the characters of its carapace, approaches more 

 nearly to the Chelone Mydas in the form of the vertebral scutes, 



