4 FOSSIL CHELONIAN REPTILES OF THE 



ginal plates, with both divisions of the first neural plate, «', with the anterior truncated 

 angle of the second neural plate, s 2, and with the second costal plate, pi. 2 ; the second, 

 pi. 2, to the seventh, pi. 7, costal plates, have the posterior angle of their mesial ex- 

 tremity truncated; they become slightly expanded at their lateral extremity; and, after 

 the third, they gradually decrease in length. The second, fourth, and sixth costal 

 plates, like the first costal plate, bear the impressions of the lines of union of the costal 

 scutes with each other and with the vertebral and marginal scutes : the third, fifth, and 

 seventh costal plates bear the impressions of the lines of union of the costal with the 

 vertebral and marginal scutes. The eighth costal plate is impressed by the line of 

 union between the fourth costal scute and the fifth vertebral scute, and by that of both 

 these scutes with the fourth vertebral scute mesially, and with the tenth marginal scute 

 laterally. 



The exterior surface of all the above-described elements of the carapace is minutely 

 wrinkled and granulated, except near the sutural borders, where it is impressed by 

 numerous close-set fine lines, directed at right angles, or nearly so, with those borders. 

 This two-fold pattern is best marked in the costal plates, in most of which the marginal 

 lineated sculpturing extends over about one fourth of the entire breadth of the scute. 

 There are no concentric impressions indicative of the lines of growth of the homy 

 scutes. 



The first marginal scutes meet at the middle line on the forepart of the nuchal 

 plate, and do not leave there any median or nuchal scute in the present species. The 

 first and second vertebral scutes are of equal breadth^ the succeeding three progressively 

 decrease in breadth : all are six-sided, and broader than they are long, the length and 

 breadth being most nearly equal in the fourth vertebral scute, v 4. 



The following are the dimensions of the principal vertebral scutes : 





First. 



Second. 



Third. 



Fourth. 





In. Lines. 



In. Lines. 



In. Lines. 



In. Lines 



Length, or antero-posterior extent 



. 2 6 



2 11 



2 11 



3 



Breadth .... 



. 4 10 



4 10 



4 7 



3 6 



Their shape is sufficiently indicated in the figure, Tab. II ; as is also that of the 

 costal scutes, c 1 to c 4. 



In the carapace above described, the greater part of the marginal plates, the eighth 

 costal plate of the right side, and the terminal neural plates, are wanting ; but sufficient 

 remains in natural juxtaposition to show that the carapace has been of a full oval 

 figure, broadest anteriorly, with a very slight degree of convexity, and without any 

 special elevations along the median line or at other parts. 



The plastron. Tab. Ill, is a long, rather narrow, flat, oval plate ; it was probably 

 rounded anteriorly, but this border is fractured : it contracts from the lateral wall, hs,ps, 



