308 PALAEONTOLOGY 



has been superseded in our hemisphere by other strata and 

 a higher type of mammalian organization. Fig. 87 repre- 

 sents a section of the strata overlying the slates whence the 

 fossil mammalian jaws, with associated Megalosaurs, Ptero- 

 dactyles, and other oolitic organisms, have been obtained at 

 Stonesfield in Oxfordshire. The vertical thickness of the strata 

 through which the shaft is sunk to the gallery is 62 feet ; on the 

 side opposite the right hand is marked the depth of the horizon- 

 tal gallery, where the slate is dug which contains the fossils ; 

 on the opposite side the strata are numbered in succession. 



Genus Stekeognathus. — The last evidence of a mamma- 

 lian animal discovered in the Stonesfield slate is of peculiar 

 interest, because it exhibits a type of grinding teeth quite dis- 

 tinct from any of the previously acquired jaws from that lo- 

 cality, and affords evidence of a 

 small vegetable-feeding or omni- 

 vorous quadruped. It consists 

 of a portion of a lower jaw, im- 

 bedded in the characteristic 

 matrix (fig. 88), about 9 lines in 

 *kj,^sm& s &^ extent, and containing three 

 ' molar teeth (a, b, c). It is nearly 



titereognathus ; portion of jaw, mi- x ^ 



bedded in oolitic matrix (nat, straight ; the side exposed is 

 Slze ) - convex vertically ; a slight bend 



downwards, and decrease of vertical diameter towards the end, 

 indicates it to be part of a left ramus. This is unusually shal- 

 low, broad or thick below, the side passing by a strong convex 

 curve into the lower part ; a very narrow longitudinal ridge, 

 continued after its subsidence by a few fine lines, forms a 

 tract which divides the lateral from the under surface; else- 

 where the bone is smooth, without conspicuous vascular 

 perforations. The depth or vertical diameter of the ramus is 

 not more than two lines. Of the three teeth remaining in this 

 portion of jaw, the middle one is the least mutilated. The 



