CHEL0NIDJ3. 



29 



the symphysis. Shell cordiform, or pointed at both extremities, with 

 four costal shields ; the plastral vacuities persisting for a long 

 period ; epiplastrals very broad ; entoplastral long and dagger- 

 shaped ; xiphiplastrals slender, and uniting only at their distal ex- 

 tremities. Coracoid long and slender, with but slight distal expan- 

 sion. Humerus (fig. 6, A) with the head placed almost directly 

 above the long axis, the shaft much flattened and scarcely curved, 

 the ulnar process rising much above the head, and the radial process 

 not connected with the head. Terminal phalangeals flattened. An 

 intergular. The skull is very small in proportion to the shell and 

 limb-bones, and the neurals of the carapace are frequently elongated. 

 For the generic synonymy of the two existing species see Bou- 

 lenger, ' Catalogue of Chelonians, &c.' p. 180. 



Fig. 9. 



B 



Outer aspect of the left ramus of the mandible of (A) Chelone mydas&nd of (B) 

 Lytoloma crassicostatum. e, postarticular process ; /, vascular foramen ; 

 g, masseteric fossa ; h, coronoid process ; p, expansion near symphysis ; 

 other letters as in fig. 8. (After Dollo.) 



