1902.] NATURAL SCIENCES OF PHILADELPHIA. 387 



tiou of hypoplasl and xiphiplast, is iu T. Carolina 5 mm. thick; iu 

 T. eunjpygia, 7 mm. thick. This border is also wider in the latter 

 species than in any specimens of the living species at hand. 



No doubt all or nearly all the characters appealed to for the 

 separation of Cope's species are more or less variable, but it appears 

 unlikely that there should be so many deviations from the normal 

 in one or two specimens. An examination of eighteen specimens 

 of T. Carolina revealed the fact that in one the fifth vertebral was 

 in contact with the ninth marginal on both sides, while in another 

 specimen these scutes were in contact on one side. In both cases, 



Fig. 7. 



however, some of the scutes in the region were somewhat abnormal 

 in their development. Leaving this out of view, we have the eon- 

 tact in about eight and one-third per cent, of cases. It appears 

 unlikely that the only two specimens that we have of the fossil 

 species would belong among this small minority. 



In the Port Kennedy specimen the anterior lobe is 51 mm. long, 

 and 68 mm. wide at the hinge. In front of the hinge the width 

 increases to 72 nnn. The posterior lobe has had a length of at 

 least 80 mm. 



Fig, 6 presents a view of the fragment of the rear of tlio plas- 

 tron of the Port Kennedy specimen, the interrupted lines having 

 been added iu order to sliow tlie- position of tlie frngmeut. The 



