CHELONIA. 21 



the hyosternals. Both hyostemals {//s) and hyposternals (ps) are slightly bent upon a 

 median longitudinal prominence of their under surfaces. 



The length of the third costal plate (jjIs) is one inch seven lines ; its antero- 

 posterior diameter or breadth, six lines : in the form of the vertebral extremities of the 

 costal plates, and of the neural plates to which they are articulated, the present fossil 

 resembles the C/iel. longiceps ; but the fifth neural plate is more convex, and is crossed 

 by the impression dividing the third vertebral scute (I's) from the fourth, which 

 impression crosses the suture between the fifth and sixth neural plates in both Chelone 

 longiceps and Chelone breviceps. Whether, in the progressive change of form, which 

 the vertebral scutes may have undergone in the growth of this young turtle, as during 

 the growth of the young loggerhead turtle {Chelone caouanna), hy an increase of length, 

 without corresponding increase of breadth, the impression between the third and 

 forth vertebral scute, might also retrograde to the interval between the fifth and sixth 

 neural plates, I am uncertain, having only had the opportunity of comparing the 

 scutes of the young and old loggerhead turtles, not the skeletons. The change in 

 the lateral angles of the vertebral scutes, resulting from the elongation of the scutes 

 themselves, in the loggerhead turtle, would be similar to that in the Chelone loiifficejjs, as 

 compared with the Chel. lafiscutafa, on the hypothesis that the latter is the young of 

 the former ; but in my present uncertainty I prefer to indicate the specimen in question, 

 by the definite name proposed in my original Memoir ; its description as a distinct 

 species being more likely to attract the attention of Collectors to similar specimens, 

 and to enable them to identify such. Figure 3 gives the degree of convexity of the 

 carapace, and the double curve of the plastron produced by the prominence of the 

 principal hsemapophyses hs ?iXi(\. ps. The left scapular arch (51) is exposed in this view. 



Chelone convexa. Oioen. Plate 14 and Plate 24, fig. 4. 



Proceedings of the Geological Society of Loudon, December 1, 1841, p. .575. Report 

 on British Fossil Reptiles, Trans. British Association, 1841, p. 178. 



The fourth species of Chelone, indicated by a nearly complete cuirass, from Sheppey, 

 holds a somewhat intermediate position between the Chelone breviceps and the Chelone 

 longicejis ; the carapace being narrower, and more convex than that of Chel. longiceps ; 

 broader and with a more regular transverse curvature than in the Chelone bre'oiceps. 



Although the specimen is equal in size to either of the two with which it is here 

 compared, the costal plates hold an intermediate length, which shows that this 

 character is not due to a difference depending upon age. 



The fossil in question includes the first to the eighth neural plate inclusive ; the 

 first plate (2) expands behind, and both posterior angles are truncated to articulate 

 with the second costal plates {pli). The second neural plate (3) is quadrate, half as 

 long again as broad, and the second pair of costal plates articulate with this, as well 



