2 CHELONIA. 



In existing forms teeth absent, and the jaws ensheathed in horn. 

 Each rib single-headed, and articulating at the junction of two 

 vertebra? : no cervical ribs l , and no transverse processes to dorsal 

 vertebra?. Terminations of vertebral centra varying greatly in con- 

 tour, even in different regions of the column of individual forms. 

 Chevrons usually absent. Pectoral girdle placed within the ribs : 

 precoracoid and scapula rod -like and fused together ; precoracoids 

 and coracoids respectively meeting in a ventral cartilaginous sym- 

 physis ; no sternum or omosternum ; clavicles and interclavicle 

 apparently represented by the epiplastrals and entoplastral. Hu- 

 merus with an ectepicondylar groove, which may be converted 



Fig. 1. 



Chelonian humeri.— The specimens belong to the left side, and are viewed from 

 the dorsal aspect; all being reduced. A. Genus non. det., from the 

 Kimeridge Clay. f. B. Chelys fimbriata, recent. C. Testudo sp., 

 recent, g, head ; h, radial process ; i, ulnar process ; e, ectepicondylar 

 canal. 



into a foramen ; limbs variable, being adapted either for walking 

 on land, or webbed, or modified into paddles ; in the latter case 

 no hyperphalangism . 



It may be observed that the humerus of existing Chelonia is 

 always characterized by its extremely prominent and subglobular 

 head, but that in certain Mesozoic forms (fig. 1, A) the develop- 

 ment of the head is much less marked, and the bone departs less 

 widely irom a more normal type. It appears from these Jurassic 

 forms that the radial process (fig. 1, h) corresponds with the deltoid 



Possibly present in Miolania. 



