50 



THE GEOLOGIST. 



intermediate position between C. breviceps and C. longiceps, 

 the carapace being narrower and more convex than in the 

 latter, and broader and with a concavity arising from a more 

 regular curvature than in the former. The true marine charac- 

 ter of this specimen is shewn in the small relative size of the 

 entire femur, which is attached by the matrix to the left xi- 

 phosternai. This fossil Mr. Owen has named C. sub- 

 convexa. 



The fifth species is separable from others by its carapace 

 more nearly approaching to that of the C. mydas in the ver- 

 tebral form of the scutes ; but still more strongly by the 

 sixth and eighth vertebral plates supporting a short, sharp, 

 longitudinal crest. Mr. Owen proposes to designate this 

 fossil C. subcristata. 



Besides these remains Prof. Owen describes a skull from 

 the same formation at Harwich, in the collection of Prof. 

 Sedgwick. Its marine nature is proved by the great expan- 

 sion of the osseous roof of the temporal fossae; and the share 

 contributed to that roof by the post frontals ; but in the obli- 

 que position of the orbits^ and the diminished breadth of the 

 interorbital space, this Chelonite, is known to approach more 

 nearly to Tryonix and Emys than the previously described 

 species. From all known existing or extinct Chelones it 

 differs in the greater antero-posterior extent and remarkable 

 flatness of the under part of the symphysis of the lower jaw. 

 This fossil Mr. Owen has named C. platygnathus. The au- 

 thor also notices a portion of the carapace of a marine turtle, 

 also from Harwich, preserved in the British Museum. 



A review of the facts detailed above leads to conclusions 

 of much greater interest than the previous opinions respect- 

 ing the Chelonites of the London Basin could have origi- 

 nated. It is obvious, when we consider that the Sheppy 

 Chelonites belong to the true marine genus Chelone, and that 

 the number of species of the Eocene extinct turtles already 



