112 BOTHREMYS. 



larger than the frontals, and arc defined from the maxillaries by an oblique suture 

 proceeding from tlie 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 PoJocnemys. 



From the broken boundary of the parietals, post-frontals, malars, and maxillaries 

 in the fossil, I suspect a bony vaidt 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 (h) 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, Avhich is almost fiat. 



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 skiUl arc as follows : — 



Lines. 



. Height of skull from a level surface 16 



Breadth of face at back part of maxillaj 32 



Length of face from fronto-parietal suture to anterior nasal orifice . . .16 



Diameter of orbits, transverse and vertical 7 



Transverse diameter of anterior nasal orifice 10 



Vertical diameter of anterior nasal orifice, each side ...... 5 



Depth of face below orbits ^^ 



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 orbits 7 



Distance of posterior nares from margin of the prema.xillaries .... 10^ 



Breadth together of the posterior nares ........ 6^ 



Breadth of base of skull between the external pterygoid processes . . .19 



Breadth of lower jaw at coronoid processes 23 



Distance from coronoid process to pointed extremity of symphysis . . .21 



Breadth of jaw at symphysis 9 



Height of jaw at back of symphysis 6 



Height of jaw at coronoid processes 13 



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 



