78 BRITISH FOSSIL REPTILES. 



further back in the orbit, and is deeper at its posterior termination, than in the 

 Chelones. In all these characters, derived from the bones entering into the formation 

 of the orbit, the fossil under comparison agrees with the Emys, and, indeed, departs 

 further from the Chelones than the Podocnevii/s ea'pama does, by the much smaller 

 proportion in which the anteriorly contracted malar bone (20) contributes to the rim 

 of the orbit. In the Tnonyces, the malar bone forms a larger proportion of the border 

 of the orbit than in the Fodocnemys expansa, and a fortiori, than in the fossil in question. 



The choice between the Fluviatile or Paludinose tribes of the fresh-water Chelonians, 

 in the determination of this fossil, is better guided by the form and proportions of the 

 skull anterior to the orbit. In the recent Trioni/ces the muzzle is more acute, and in 

 most of them more prolonged than in the Eraydians, with which the fossil skull 

 agrees in the shortness of the muzzle ; whilst it departs further than most recent 

 Emydians from the Trionycida, in the broad truncated character of its anterior termi- 

 nation. There is also a very well-marked character of affinity to the Fodocnemys 

 expansa, in the smooth and shallow canal which extends from the fore part of the 

 orbit forwards to the border of the external nostril across the upper part or nasal process 

 of the superior maxillary bone (21). This groove is very accurately represented in fig. 1 , 

 PI. 40, in the fossil ; it is rather broader in proportion to its length in the Fodocnemys 

 expansa; but so far as it has depended upon the presence and arrangement of the 

 facial scutes, it is decisive against the fossil having appertained to any species of soft 

 turtle (Trionyx), in which such epidermal parts were entirely wanting. 



The marks of the supracranial scutes in the fossil are, as in some Emydians, too 

 feebly and obscurely traceable to permit of a satisfactory comparison of their arrange- 

 ment. The exterior surface of the prefrontal (16), frontal (11), postfrontal (12), and 

 parietal (7) bones is subrcticulate. The substance of the bones is thick and coarsely 

 cancellous. The nasal bone is connate with the prefrontal, as in most modern Emydians ; 

 in the proportion of this compound bone the fossil resembles more the ordinary 

 Emydians {Emys europcsa, e. g.) than it does the Fodocnemys expansa. The border of 

 the prefronto-nasal forming the upper part of the nostril is thick and rounded ; as is 

 also the lateral border of the same cavity formed by the maxillary. The lower part 

 of this border of the maxillary shows the suture for the premaxillary, which must 

 have presented similar proportions to the premaxillary of the Fodocnemys expansa and 

 other Emydians. The shape of the frontal (11), the proportion of the upper border of 

 the orbit which it forms, and the course of its sutures with the contiguous bones, are 

 clearly indicated in fig. 2, PI. 40. The straight line formed by the suture between the 

 frontal (11) and postfrontal (12) resembles that in the Fodocnemys expansa; it is bent 

 or curved in the Chelones. To what extent the postfrontal (12) was continued backwards, 

 whether so, as with the parietal, to roof over the temporal fossa, as in the Fodocnemys 

 expansa* or, in a less degree, leaving that fossa open superiorly, as in the Emydians 



* See Cuvier, loc. cit., pi. xi, fig. 1 a. 



