THE CORALLIAN ROCKS OF WEYMOUTH. 399 



having been accomplished, the trouble expended upon it was repaid by 

 the peculiar characters of its front end, which were thereby displayed. 

 The fracture and displacement of the right ramus is shown also in this 

 view (fig. 2). The superior size of the 2nd, 3rd, 4th, and 5th alveoli 

 is well seen, as well as the remains of teeth which several of them 

 contain. In order, apparently, to accommodate these larger teeth, 

 the jaw is wider in this region than in that which is immediately 

 behind it, where the alveoli are smaller. On each side, just within 

 the large alveoli, there is a deep groove, extending from the front 

 backwards to the fifth or sixth tooth. The inner edge of the alveolar 

 border in this region is on a level with the median area of the jaw, 

 as shown by a transverse section, figure 3, while its outer edge is 

 depressed, so that the general plane of this border forms an angle of 

 about 15° with that of the median area. Behind the fifth tooth, the 

 alveolar border, while retaining the same general direction, becomes 

 rapidly lowered until its inner edge is on a level with the bottom 

 of the groove, so that the groove having lost one of its sides, be- 

 comes a kind of step, and a transverse section in this region has the 

 appearance shown in figure 4. The median area is almost flat, each 

 half, however, being slightly rounded. The most remarkable pecu- 

 liarity of this jaw is the manner in which about two inches of the 

 anterior part of the median area becomes separated from the hinder 

 portion, in the form of a spindle, by deep oblique grooves. These 

 grooves pass from the lateral ones opposite the third pair of teeth, 

 and meeting in the middle line dip down into the substance of the 

 jaw or, rather, into a channel which appears to have existed in the 

 symphysis. The spindle-shaped area is longitudinally grooved; 

 whilst the area immediately behind the oblique grooves, although 

 somewhat broken, gives evidence of having possessed a longitudinal 

 ridge close to the symphysial suture. 



The teeth are fragmentary ; but still, from what remains of them, 

 several of their characters may be made out. Allusion has already 

 been made to the fact that the 2nd, 3rd, 4th, and 5th teeth upon 

 each side are larger than the others. In two or three instances the 

 young teeth may be seen within the broken roots of the mature 

 ones. The bases of the largest teeth must have had a diameter of 

 at least half an inch ; and, judging from an impression in the matrix, 

 they projected about an inch and a quarter above the margin of the jaw. 

 This impression also shows that there was no very marked division 

 between the crown and the fang of the tooth, the former, however, 

 being distinguished by the possession of fine, but very distinct 

 longitudinal ridges. In transverse section the greater part of the 

 tooth appears to have been circular ; but the apex of a young unused 

 tooth which is well preserved in the third alveolus of the left ramus 

 is slightly compressed, having a distinct ridge running down each 

 side, and two smaller ridges on the inner face ; a transverse section 

 near the apex would give an outline as in figure 5 b. 



With regard to the length of the symphysis, one cannot speak 

 with certainty, on account of the parts being displaced ; but while 

 it seems extremely probable that it extended at least as far as the 



