298 TERTIARY VERTEBRATA OE THE FAYtM, 



short pedicle and is considerably below the level of the lower border of the com- 

 pletely closed tympanic ring, which is oval in outline. So far as can be determined, 

 the form and relations of the squamosal, quadrato-jugal, and jugal do not differ 

 in any important respect from those of the same elements in JPodocnemis, and the 

 same may be said for the bones of the side of the cranium. The large foramen 

 sphenoidale (f-s.) is shown in PI. XXV. fig. 1, opening in front of the epiotic. 



The symphysial region of the mandible (PL XXV. fig. 3, sym.) is very large and 

 massively constructed. In form it is roughly pentagonal, the two anterior sides 

 forming the labial borders, the two laterals being produced upwards into strong 

 pointed coronoid processes (cor.), while the posterior side is slightly concave. This 

 posterior border is greatly thickened and deeply grooved ; in front of it the bone 

 thins gradually towards the labial borders. The lateral edges of the symphysis are 

 also deeply grooved {m.g.), the groove being continued back on to the rami as far as 

 the articulation. The ventral surface of the symphysis is very slightly convex in all 

 directions ; it is separated from the ventral surface of the rami by shallow grooves, 

 and probably was covered by a single large horny plate. The rami are not only 

 deeply grooved on the outer face, as already mentioned, but are also hollowed on the 

 inner side. The ai'ticular surface {art.) for the quadrate is large ; it is convex from 

 side to side and slightly concave from before backwards : behind it there is a blunt 

 angular process {ang.), the upper surface of which is concave. 



The extraordinary massiveness of the symphysis and the great development of the 

 processes and grooves for the attachment of the jaw-muscles indicate that the jaws 

 with their horny covering must have formed a very powerful crushing-apparatus. 

 A similar modification is observable in some Cyptodiran tortoises, e. g. Lytoloma, 

 described and figured by Dollo *. 



Although in no case have the carapace and plastron been found associated with 

 the skull in such a manner as to leave no doubt that they belong to the same 

 individual, nevertheless the shell now to be described may be regarded with reasonable 

 certainty as belonging to the present species. In the first place, this form of shell, like 

 the skull, is the commonest occurring in the Qasr-el-Sagha beds, and in the second 

 place it differs widely from the shell of Podocnemis, the only other Pleurodiran genus 

 found at this horizon. 



The most nearly complete specimen is a somewhat crushed shell (text-fig. 96), 

 both carapace and plastron being so coated with gypsum that many of the sutures 

 and most of the grooves between the epidermal plates cannot be seen. The carapace 

 (text-fig. 96, A) is depressed, this being in part due to crushing, though it is clear 

 that the shell was much wider and less convex than in the next species, S. libyca, 

 approaching in this respect S. podocnemioides as described by Eeinach. The number 



* Bull. Mus. Eoy. Hist. Nat. BeJge, vol. iy. (1886) p. 129. See also Lydekker, Proe. Zool. 8oc. 1889, 

 p. 60. 



