STEREOGXATHUS. 345 



sphere by other strata and a higher type of mammalian 

 organization. Fig. 114 represents a section of the strata 

 overlying the slates whence the fossil mammalian jaws, with 

 associated Megalosaurs, Pterodactyles, and other oolitic or- 

 ganisms, have been obtained at Stonesfielcl 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 horizontal gallery, 

 Avhere the slate is dug which contains the fossils ; on the 

 opposite side the strata are numbered in succession. 



Genus Stereognathus. — This mammalian animal, from 

 the Stonesfielcl slate, exhibits a type of grinding teeth distinct 

 from that in any of the previously acquired jaws from secon- 

 dary strata, and appears to have 

 been a small vegetarian or om- 

 nivorous quadruped. It is known 

 by a portion of a lower jaw, im- 

 bedded in the characteristic ma- 

 trix, and three molar teeth (fig. 

 115, a, b,-c). The crown of the 

 tooth (fig. 116, B) is of a quadrate 



P „ .,,. . i «i --it Stereoqnathus : portion of jaw, im- 



form, 3 millimetres by 3# milli- be dded in oolitic matrix (nat. 

 metres, of very little height, and slze ^ 

 supports six subequal cusps in three pairs, each pair being 

 more closely connected in the antero-posterior direction of the 

 tooth than transversely. 



The outer side of the crown (fig. 115, 5), supported by a 

 bifurcate fang which contracts as it sinks into the socket, 

 shews two principal cusps or cones, and a small accessory 

 basal cusp. The cones are subcompressed, and placed obliquely 

 on the crown, so that the hinder one (o, fig. 116) is a little 

 overlapped externally by the front one, o, the fore part of the 

 base of the hinder one being prolonged inwards on the inner 

 side of the base of the front cone. The two middle cones 



