fro}ii the London Clai/. 231 



orbit to the nares is -^ ot" an inch. Thr parietal and frontal 

 bones are deej)ly marked with scutes, which are iTpresented 

 in Prof. Owen's tiLCure. Tlie head widens to not less tlian 

 5^ inches ; but the ([ua(hato-jugal (scpuiniosal, Owen) and 

 scjuaniosal (mastoid, (.)wen) are imperfectly preserved. The 

 squamosal bone extends further outward, and looks upward 

 more than in marine Chelonians. It apj)ears to terminate 

 behind in a thin tihn, as in C caouanna. In transverse sec- 

 tion the parietal region is similar to tliat of marine Chelnnians, 

 only broader. 



The (juadrate bone is more conically excavated than in the 

 recent types, but otherwise similar. 



So far as they are exposed, the basiocci])ital, exoccipital, 

 supraoccipital, and paroccipital, Owen, offer no variations 

 from tlie ordinary type. From the base of the tripartite 

 occij>ital condyle to the top of the spine of the supraoccipital 

 is 2\ inches. 



The lower jaw is remarka1)ly flattened on the under side. 

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

 side. TI*e sym})hysis 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 

 Trionyjc ; and it is sliown in Mr. Dinkel's plates to Prof. 

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

 fig. 3) and CheJone 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 sm'angular 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. (_)n the palatal surface they are fractured, and 

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

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

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

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

 represented in one bone. 



The only species from the London Clay whicli 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 



