OOLITIC FORMATIONS. 19 



left ramus : the inclination of the cusps of the teeth (figs. 27, 28) towards the opposite 

 end might, indeed, be deemed evidence of its belonging to the right ramus ; but neither 

 this degree of inclination nor the position of the accessory cusp (fig. 29, a) is decisive of 

 the way in which that end of the fragment points. Not more of the matrix could be safely 

 meddled with, on the small chance of further evidence to this comparatively unimportant 

 particular being had ; and the description of the fossil assumes that the shallower end is 

 the front one, the deeper one (a) the hind end of the fragment, and that it is part of the 

 left ramus of the mandible. 



This ramus is unusually shallow, and 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 smface ; elsewhere the bone is smooth, without conspicuous vascular perforations. 

 The depth or vertical diameter of the ramus is not more than two lines. 



This portion of jaw contains three teeth, the middle one of which is the least muti- 

 lated ; and, by carefully removing the matrix which partly covered its crown, I exposed 

 the whole of its singularly modified grinding surface. The first of the three teeth 

 (fig. 27, a) appears to have been smaller than the others, but its crown has been too 

 much broken to show its original characters. The third tooth (c) is less mutilated : it is 

 of the same size and had the same structure as the middle one (6). Of this tooth, fig. 

 30 shows the grinding surface magnified about five diameters. It is of a quadrate form, 

 three millimeters by three and a half millimeters, of very little height, and supports six 

 subequal cusps, in three pairs, each pair being more closely connected in the antero- 

 posterior direction of the tooth than transversely. In the Plate its position is at right 

 angles to that in the jaw, fig. 27. 



The outer side of the crown (fig. 29), supported by a narrow fang which contracts 

 as it sinks into the socket, shows two principal cusps or cones (o, o) and a small (anterior) 

 accessory basal cusp {a). A small portion of the outer side of the anterior cone (o) has been 

 chipped off; that of the second cone [o) shows a well-marked convexity. The hard and 

 shining enamel which covers these parts of 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 is a little overlapped externally by the front one, the 

 fore part of the base of the hinder one being prolonged inward on the inner side of the 

 base of the front cone. The two middle cones are subcompressed laterally, with the fore 

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

 inner surface (fig. 28) convex, with their summits slightly inclined forward; a small 

 portion of enamel has been chipped off the hinder lobe. The fore part of the base of 

 the hinder cone is prolonged obliquely towards the centre of the crown, beyond the con- 

 tiguous end of the base of the front cone, so as to cause an arrangement like that of the 

 two outer cones ; the obliquity of the posterior cone of both the outer and the inner pairs 

 being such that they slightly converge as they extend forward. 



