CHELONIA. 17 



In a second example of the skull of Chelone longiceps, two of the middle neural 

 plates, and the corresponding costal plates of the right side, portions of vertebrae, 

 with the right xiphisternal piece, humerus and femur, are cemented together, and to 

 the cranium by the petrified clay. (T. IV, fig. 1.) 



The neural plates (s2, S3) are flat and smooth ; the entire one measures one inch 

 two lines in length, and nine lines across its broad anterior part :■ — -this receives the 

 convex posterior extremity of the preceding plate in a corresponding notch. A small 

 proportion, about one sixth, of the anterior part of the external margin, joins the second 

 costal plate {ph) ; the remaining five sixths of the outer margin forms the suture for 

 the vertebral end of the third costal plate {ph). 



In this respect, the Cliel. longiceps resembles the existing Chelones ; and differs, as 

 well as in the smooth and flattened surface of the vertebral plates, from the Chelone 

 breviceps. The length of the third costal plate, in the fragmentary example here 

 described, is three inches ; the impression of the commencement of the narrow portion, 

 formed by the extremity of the coalesced rib, is preserved. 



The marginal indentations of the vertebral scutes are not half a line in breadth. 



The transverse impression between the first and second vertebral scute crosses the 

 first neural plate, nine lines from its posterior extremity ; the second neural plate is 

 free, as in other Chelones, from any impression, being wholly covered by the second 

 vertebral scute. 



The expanded ribs are convex at the under part, slightly concave at the upper 

 part in the direction of the axis of the shell ; they slope very gently from the plane of 

 the neural plates, about half an inch, for example, in an extent of three inches ; thus 

 indicating a very depressed form of carapace. 



The xiphisternal bone (xs), like that of Chel. breviceps, is relatively broader than in 

 the existing turtles, and both the internal and external margins of its posterior half 

 are slightly toothed. A part of the notch by which it was attached to the hyposternal 

 remains upon the broken anterior extremity of the bone. It measures one inch 

 two lines across its broadest part ; its length seems to have been three inches and a 

 half. 



The humerus presents the usual characters of that of the Chelones ; its length is 

 two inches three lines ; its breadth across the large tuberosities ten lines. The radius 

 and ulna extend in this Chelonite from beneath the carapace into the right orbit ; the 

 radius is one inch and a half in length ; the ulna one inch, three lines in length ; 

 portions of vertebrae adhere also to the mass, the state of which indicates that the 

 animal had been buried in the clay before the parts of the skeleton had been wholly 

 disarticulated by putrefaction. 



A mass of Sheppey clay-stone supporting the ninth- and tenth neural plates, and the 

 expanded portions of the sixth, seventh, and eighth costal plates of the right side, 

 exhibits the characters of the marine turtles in the great relative expansion of the 



