WEALDEN CHELONIANS. 181 



in length. The second, fourth, and sixth costal plates, Hke 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 mai'ked 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 fines of growth of the horny scutes. 



The first marginal scutes meet at the middle fine 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 : 



Their shape is sufficiently indicated in the figure (Plate 53) ; as is also that of 

 the costal scutes c l 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 terminual 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 (Plate 54) is a long, rather narrow, flat, oval plate; it was 

 probably rounded anteriorly, but this border is fractured : it contracts from the 

 lateral wall {h s, p s) with a gentle sigmoid marginal curve to the hinder apex {x s), 

 which is notched. The middle third of each lateral border of the plastron is 

 connected, through the medium of three marginal plates, with the carapace. The 

 length of the plastron, as far as it is entire, is 13 inches ; its breadth, at the fore 

 part of the lateral walls, is 6 inches 6 lines. 



