30 FOSSIL REPTILIA OF THE LONDON CLAY. 



The right coracoid (52) is exposed by the removal of the right hyosternal ; it differs 

 in form from that preserved in the large specimen of Chelone planhnentum, in Professor 

 Sedgwick's Museum, in expanding less suddenly at its sternal end, as compared with 

 the coracoid of the Clielone mydas, or with that of the Chehne caouanna, which is 

 somewhat broader than in the Chel. mydas ; the coracoid of the Chel. crassicostata 

 agrees with that of the Chel. planimentum in the greater degree of its expansion. At 

 the anterior fractured surface of Mr. Dixon's Chelonite, the long and slender columnar 

 or rib-like scapula, is shown, extending from the under part of the head of the second 

 costal rib downwards and outwards, for an extent of two inches, and then sending its 

 acromial or clavicular prolongation at the usual open angle downwards and inwards 

 to rest upon the episternal. The proportions of these parts of the scapular arch are 

 quite those which characterise the genus Chelone, but they do not supply such marks 

 of specific distinction as the coracoid element does. 



Chelone declivis. Owen. Tab. XIV. 



The extinct turtle represented by this specimen, and indicated by the above term, 

 bears the same relation to the Chelone convexa, which the Chelone longiceps* does to the 

 Chelone laiiscuiata ;f that is, it has the same general characters of the petrified parts of 

 the carapace, but differs in the narrower proportions of the vertebral scutes (ui — va), and 

 the more open angle at which their two lateral borders meet ; the vertebral angles of 

 the costal scutes being correspondingly less acute. 



The specimen is from the Eocene deposits of Bognor, Sussex, and is preserved in 

 the collection of Frederick Dixon, Esq. It consists of the seven anterior neural plates, 

 and the corresponding seven pairs of costal plates (T. XIV), those of the right side 

 having been broken away from their attachments to the neural plates, and bent upon 

 the rest of the carapace at an acute angle with some slight separation of the sutures 

 of the costal plates (fig. 2). 



The neural plates correspond in general form with those of the Chelone convexa, the 

 hind ones being rather broader ; the first (si) is crossed at its middle part by the 

 impression dividing the first (vi) from the second (v2) vertebral scute ; the second neural 

 plate (s2) is an oblong four-sided one, with both ends of equal breadth. The third neural 

 plate, S3, resumes the hexagonal figure with the broadest end, and two shortest sides 

 at the fore part ; and is crossed in its lower half by the impression dividing the second, 

 v2, from the third vertebral scute, V3. The fifth neural plate (so) is crossed by the next 

 transverse impression nearer its lower border. The sixth and seventh neural plates 

 retain the same form and proportions as in the Chelone convexa, except a somewhat 



* Proceedings of tine Geological Society of London, December 1, 1841, p. 572. 

 •f Ibid., p. 5/4. 



