CHELONIA. 51 



A well-marked distinctive character is also afforded by the seventh costal plate 

 {pi'), from which the free end of the connate rib projects at the anterior angle of the 

 dilated end in Tri. Barbara, and the free border of that end describes a straight line 

 transverse to the axis of the carapace. 



The free borders of the eighth pair of costal plates are on the same transverse line, 

 and the posterior part of the carapace is censequently truncate and straight. 



The lateral margin of the carapace is more gradually bevelled dowTi, and to a less 

 obtuse edge than in the Tri. Henrici. 



The length of the carapace of the Tri. Barbarce, from the fore part of the first 

 neural plate to the hind border, is nine inches and a half ; the greatest breadth of the 

 carapace, in a straight line across the fourth pair of costal plates, is nine inches ten 

 lines. The total length of the carapace is eleven inches and a half. 



The free end of the connate rib projects entire from the fifth, sixth, and seventh 

 costal plates. 



The character of the sculpturing of the outer surface of the costal plates is very 

 similar to that in the Tri. Henrici : the tendency to the concentric arrangement of 

 the raised lines is equally well marked in Tri. Barbara, and is accurately given in Mr. 

 Erxleben's beautiful plate. 



The carapace is not only more arched transversely, but it differs from that of 

 Tri. Henrici in being slightly depressed along the middle line, as is indicated in fig. 2, 

 PI. 5. 



This beautiful species of Triomjx is dedicated, with much respect, to its accomplished 

 discoverer, Barbara, Marchioness of Hastings, and Baroness Grey de Ruthyn. 



Trionyx incrassatus. Owen. Plates 26, 27, and 28. 



This species of Trionyx, from Eocene formations of the Isle of Wight, resembles in 

 general form the Tri. Henrici of the Hordwell sand, but differs from it in the anterior 

 internal angle of the first costal plate {ph. Pis. 26 and 27) being cut off, like that 

 of the second and succeeding costal plates : it also differs in the greater length of the 

 second costal plate as compared with the breadth of its outer end, and in the greater 

 breadth of the outer end of the sixth costal plate {ph, PI. 26), the outer or terminal 

 border of which is more convex. The nuchal plate {cli, PI. 27) articulates with the 

 whole anterior border of the first neural (s\ ) and costal plates {'ph), but sends backwards 

 a process from near the middle of its posterior border, which fits into the space left 

 between the truncated antero-internal angles of the first costal plates and the first neural 

 plate. In this respect it resembles the nuchal plate of Tri. Barbara (PI. 5), but the 

 difference of general shape between this more delicately formed species, and the one 

 under consideration, is well marked, and decisive as to their specific distinction. The 



