STEREOGNATHUS 



309 



crown of this tooth (fig. 89, B) is of a quadrate form, 3 milli- 

 metres by 3^ millimetres, of very little height, and supports 

 six subequal cusps in three 

 pairs, each pair being more 

 closely connected in the an- 

 tero-posterior direction of the 

 tooth than transversely. 



The outer side of the 

 crown (fig. 88, &), supported 

 by a narrow fang which con- 

 tracts as it sinks into the 

 socket, shows two principal 

 cusps or cones, and a small Fig. 89. 



accessory basal cusp. The Stereognathus; upper view of portion 



, , , , . . , of jaw (nat. size), and magnified view 



hard and sliming enamel of the miJdle tooth) B (Stonesfleld 

 which covers these parts of Oolite). 



the crown contrasts with the lighter cement that coats the root. 

 The two outer lobes or cones are subcompressed, and placed 

 obliquely on the crown, so that the hinder one (o', fig. 89) 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 

 (h, z) are subcompressed laterally, with the fore part of their 

 base a little broader than the back part. The two inner cones 

 (jp, p) have their inner surface convex, with their summits 

 slightly inclined forwards. The fore part of the base of the 

 hinder cone is prolonged obliquely towards the centre of the 

 crown, beyond the contiguous end of the base of the front cone, 

 so as to cause an arrangement like that of the two outer cones 

 (o, o'), the obliquity of the posterior cone of both the outer and 

 the inner pairs being such that they slightly converge as they 

 extend forwards. 



This type of tooth differs from that of all other known recent 

 or extinct Mammals. The noamst approach to it i* made by 



