CHELONIA. 25 



The length of the present fossil carapace, to the tenth neural plate, inclusive, 

 is nine inches. 



The breadth between the ends of the third costal plates, in a straight line, is six 

 inches six lines. The succeeding costal plates more gradually decrease in breadth, 

 than in the Chel. longiceps and Cliel. convexa ; and the entire carapace more resembles 

 in form that of the Chel. mydas, and Chel. caouanna. 



The epidermal scutes are defined by deep impressions, and as wide, relatively, as in 

 the Chel. mydas and Chel. convexa. The length of the second vertebral scute is two inches 

 one line ; its breadth is two inches two lines ; the length of the fourth vertebral scute 

 is two inches three lines ; and its breadth one inch eleven lines, and, at its posterior 

 margin, only nine lines. This scute is narrower than in Chel. caouanna, or any of the 

 previously described fossil species ; the outer angles are less produced than in the 

 Chelone caouanna. 



Sufficient of the plastron is exposed in the present fossil to show by its narrow 

 elongated xiphisternals {xs), and by the wide and deep notch in the outer margin of 

 the conjoined hyostemals and hyposternals {hs and/**^), that it belongs to the marine 

 Chelones. The xiphisternals are articulated to the hyposternals by the usual notch or 

 gomphosis ; they are straighter and more approximated than in the Chel. mydas and 

 Chel. caouanna. The external emargination of the plastron between the hyosternals and 

 hyposternals, differs from that of the recent turtles in being semicircular, instead of 

 angular ; the Chel. subcristata approaching, in this respect, to the Chel. hreviceps. 

 The shortest antero-posterior diameter of the conjoined hyosternals and hyposternals 

 is two inches seven lines. The length of the xiphisternal is two inches six lines ; 

 the breadth of both, across their middle part, is one inch three lines. 



The name proposed for this species indicates its chief distinguishing character, 

 viz., the median interrupted carina of the carapace, which may be presumed to have 

 been more conspicuous in the horny plates of the recent animal, than in the supporting 

 bones of the petrified carapace. 



Chelone planimentum. Owen. Tab. IX and X. 



Proceedings of the Geological Society of London, December, 1841, p. 576. Report 

 on British Fossil Reptiles, Trans. British Association, 1841, p. 1/8. 

 Syn. Chelone Harvicensis, Woodward (!). 



The skull of a large Chelone (T. IX) from the Eocene clay near Harwich, in Professor 

 Sedgwick's collection at Cambridge, resembles, in the pointed form of the muzzle, the 

 Chel. lonyiceps of Sheppey ; but differs in the greater convexity and breadth of the 

 cranium (fig. 2) ; and the more abrupt declivity of its anterior contour (fig. 3), and 

 from other Chelones by the broad expanse of the inferiorly-flattened symphysis menti 



(fig- !)• 



4 



