112 BOTHREMYS. 
larger than the frontals, and are defined from the maxillaries by an oblique suture 
proceeding from the nasal orifice to the inner and lower part of the orbit. 
The post-frontals are broken away at their back part; their fore part forms the 
supero-external fifth of the orbits. 
The back part of the malars is likewise broken; their fore part forms a narrow 
plate introduced between the post-frontal and posterior portion of the maxillary 
bone, as in Podocnemys. 
From the broken boundary of the parietals, post-frontals, malars, and maxillaries 
in the fossil, I suspect a bony vault to have enclosed the temporal fossa, as in 
Podocnemys and the marine Turtles. 
The mandible or lower jaw (Figs. 5, 8), as in the case of the upper maxillary 
bones, is remarkable for the deep pit (+) which occupies it on each side. ‘The 
bottom of the pit corresponds with the posterior extremity of the dentary bone, 
and it expands, trumpet-like, obliquely forward and inward upon the upper surface 
of the mandible. The boundaries of the mouth of the pit correspond with the 
anterior and posterior dental ridges extending from the symphysis and meeting at 
the coronoid process. 
The anterior dental ridge is directed forward and not upward in the usual manner. 
It is nearly on a level with the base of the jaw, which is almost flat. 
The coronoid process is as robust and prominent as in the soft-shelled Turtles or 
Trionyces. Just back of its base is situated, as usual, the foramen for the inferior 
maxillary nerve, which likewise, as in other Turtles, communicates with a groove 
on the inner side of the ramus of the jaw. 
The connections of the dentary with the other bones of the jaw are too obscure 
in the fossil to be traced with success, 
Measurements obtained from the fossil skull are as follows :— 
Lines 
Height of skull from a level surface’. : ‘ : : : : : . 16 
Breadth of face at back part of maxille —. : ; : . 32 
Length of face from fronto-parietal suture to anterior neal jorines : : eee NG: 
Diameter of orbits, transverse and vertical . : : : : 4 : ah venlh 
Transverse diameter of anterior nasal orifice : : : F ; : Sk 
Vertical diameter of anterior nasal orifice, each side 5 
Depth of face below orbits . 92 
Breadth of face between orbits 8 
Length and breadth of each frontal bone 6 
Length of fronto-nasals 9 
Breadth of fronto-nasals at lower margin of brits 7 
Distance of posterior nares from margin of the pee ch 103 
Breadth together of the posterior nares 64 
Breadth of base of skull between the external nea processes 19 
Breadth of lower jaw at coronoid processes 23 
Distance from coronoid process to pointed extremity of ante ; 2 
Breadth of jaw at symphysis : : : ; ; , : ; : yO 
Height of jaw at back of symphysis . 3 : : : ; : : BG 
Height of jaw at coronoid processes . ~. : é : a : : oan ls. 
The question may arise whether the fossil skull belongs to any of the preceding 
Turtles, and if so, to which. As it is impossible, under present circumstances, to 
