4 EOSSIL REPTILIA OF THE 



the accuracy of the drawings as an excuse for omitting any detailed description of the 

 rare fossil, I was at first inclined to infer the existence of an extraordinary anomaly in 

 the construction of this extinct Chelonian of the Cretaceous period ; but, having more 

 pleasure in the contemplation of the harmonies and constants of Nature than her 

 wonders, it was with no regret that I found that the error or lusus lay with her 

 illustrator, and not with his subject, as I have ascertained by a careful inspection of 

 the original. The artist has supplied the additional ribs from his imagination ; and in 

 the view, in fact, in which his attention was kept more closely to the parts, as in that 

 of the upper surface of the same carapace (PI. XI, Phil. Trans., 1841), he gives the 

 true number of 8 pairs of carapacial ribs or costal plates ; and the author, in refer- 

 ence to the characters of the carapace "as shown in plate XI," states, that " it is 

 composed of eight ribs on each side the dorsal ridge." The correct view of the 

 under surface of the carapace is given in T. II, fig. 1 of the present Monograph. 



Chelone Benstedi, Owen. T. I, II, and III. 



Syn. Emys Benstedi, Mantell, Philosophical Transactions, 1841. 



Chelone Benstedi, Owen. Report of British Fossil Reptiles, in ' Reports of the British 



Association,' 1841, p. 173. 



The fossil in question consists of nearly the whole carapace (T. I), and a 

 considerable portion of the plastron (T. II, fig. 2), with a coracoid bone (T. II, 

 fig. 2, 52, 53). 



The carapace includes all the neural plates; the usual number, viz., eight pairs 

 of costal plates (pi. l— 8, T. I) ; and the entire border of marginal plates, save the 

 nuchal and two or three succeeding ones. In the plastron (T. II, fig. 2), the 

 hyosternal (hs) and hyposternal (pi) bones may be distinguished. The general form 

 of the carapace is elliptical, terminated by a point at the narrower posterior end, 

 which, however, is less contracted than in some other Chelones. It is as depressed as 

 in Chelones generally, as is shown in the side view T. I, fig. 2. To judge from the 

 unmutilated and exposed neural plates, which are the first, the second, and the sixth 

 to the tenth inclusive, the carapace appears to have been traversed by a median longi- 

 tudinal crest, from which the sides gently slope with a slight convex curvature, as in 

 Chelone my das. 



The more immediate indications of the close affinity of the fossil to the marine 

 Turtles, are given by the incomplete ossification of the costal plates and of the 

 elements of the plastron ; the latter being in consequence dislocated from each other ; 

 and more especially by the shape and size of the marginal plates (T. II, fig. 1, 6, 7, 8, 9) 

 attached to the third, fourth, fifth, and sixth ribs ; as also by the form and length of 

 the coracoid bone. 



