from the London Glatj. 231 



orbit to the nares is -^ of an inch. The parietal and frontal 

 bones are deeply marked with scutes, which are represented 

 in Prof. Owen's figure. The head widens to not less than 

 5^ inches ; but the quadrato-jugal (squamosal, Owen) and 

 squamosal (mastoid, Owen) are imperfectly preserved. The 

 squamosal bone extends further outward, and looks upward 

 more than in marine Chelonians. It appears to terminate 

 behind in a thin film, as in G. caouanna. In transverse sec- 

 tion the parietal region is similar to that of marine Chelonians, 

 only broader. 



The quadrate bone is more conically excavated than in the 

 recent types, but otherwise similar. 



So far as they are exposed, the basioccipital, exoccipital, 

 supraoccipital, and paroccipital, Owen, offer no variations 

 from the ordinary type. From the base of the tripartite 

 occipital condyle to the top of the spine of the supraoccipital 

 is 2^ inches. 



The lower jaw is remarkably flattened on the under side. 

 In front of the articulation it measures 4^ inches from side to 

 side. The symphysis is not less than 2^ inches long. An 

 obscure suture divides the dentary bone into two parts : 

 Wagler figures a like condition in some recent species of 

 Trionyx] and it is shown in Mr. Dinkel's plates to Prof. 

 Owen's monograph, representing Chelone crassicostata (t. xi. 

 fig. 3) and Chelo)ie convexa (t. vii. fig. 3), but does not occur in 

 the recent marine Chelonia. The lower jaw is not deep from 

 above downward. From the margin of the surangular bone 

 (which in recent species is usually compressed at the upper 

 part) a thin process of bone, an inch long and half an inch 

 wide, is directed upward, outward, and backward towards the 

 malar bone. The ramus measures rather less than 5 inches 

 from front to back. Behind the skull are seen the well ossi- 

 fied hyoid bones ; they form on each side of the occipital 

 region a broad, thin, oblique sheet of flat bone, extending 

 from the upper margin of the squamosal bone and approxi- 

 mating to the palate, where (as preserved) they meet or over- 

 lap mesially. On the palatal surface they are fractured, and 

 appear there to be about f of an inch thick. So much as is 

 preserved on each side is 4 inches long and fully 1^ inch wide. 

 The outer margin of each is convex. With the exception of 

 the basihyal, I suppose all the hyoid elements to be here 

 represented in one bone. 



The only species from the London Clay which this resem- 

 bles is Chelone plana (Kcenig) [Chelone crassicostata^ Owen], 

 which, however, is represented as having but ten neural plates 

 instead of eleven. It has but eight pairs of ribs attached to 



