90 MR. E. T. NEWTON ON A MEGALOSAUROID JAW [Fcb. 1 899, 



the alveolar margin, 1-45 inch (87 mm.) immediately behind the 

 anterior largest tooth, and a little less about ''A inches farther back. 

 The entire bone is naturally narrow, but this narrowness has 

 probably been exaggerated by the pressure which it has undergone 

 in the rock. The lower margin, which is remarkably straight for 

 the greater part of its length, has its anterior sixth curved upward 

 till it reaches the alveolar margin. The lower edge of the bone is 

 rounded and not more than -3 inch (8 mm.) thick at its widest 

 part, which is about the middle of the bone, and thence it decreases 

 regularly to the hindermost angle, where it is merely the lower 

 edge of the thin vertical bone forming the outer plate of this 

 part of the jaw. The outer portion of this bone stands about 

 \ inch higher than the inner part, thus forming a parapet, 

 within which 16 or perhaps 17 alveoli may be counted. The 

 osseous divisions between the alveoli form triangular masses, as 

 seen on the inner aspect, the broad bases of which are marked off 

 from the inner margin of the jaw bj a longitudinal groove. In 

 this groove, and opposite the middle of each alveolus, there is a 

 small pit, in which the successional teeth make their appearance, 

 as may be seen at the bases of the fourth and of the hindermost 

 large teeth (PI. X, figs. 1 a-b & 4). The front half of the inner 

 aspect of this jaw is so like that of Megalosaurus, except for size, 

 that the description of the latter given by Auckland ^ would apply 

 very well to the present specimen. 



Between 4 and 5 inches of the hinder part of the inner side 

 of this dentary bone is occupied by a large triangular cavity, such 

 as is common in reptilian jaws ; the upper margin of this cavity is 

 sharply defined by the inner alveolar plate, which forms a wide 

 band below the alveolar margin, and, extending forward, becomes 

 somewhat broader in the region of the symphysis. Posteriorly and 

 inferiorly this alveolar plate is separated from the outer plate of the 

 bone, by an extension of the triangular cavity upward between 

 them ; but, passing forward, this separation lessens, and then 

 becomes a groove which extends forward to the symphysis. Near 

 its anterior extremity a large foramen opens into this groove. 

 Inferiorly the triangular cavity has a less distinct boundary; it 

 is formed by a thickening of the lower edge of the outer plate, 

 which increases in depth as it passes forward, and at the place 

 where it approaches the alveolar plate to form the anterior point of 

 the triangle there is a foramen penetrating the substance of the 

 bone. This triangular cavity is similar to what is found in the 

 crocodile, and doubtless, as in that creature, was covered by a splenial 

 bone extending far forward, thus converting the groove into a 

 covered canal for Meckel's cartilage. There is a slight flattening 

 of the front part of the inner surface, but it does not give one the 

 impression that the two dentary bones met in a definite symphysis. 



The cast of the anterior half of the outer surface (PI. X, fig. 2) 

 presents some peculiarities which it will be well to notice ; it is com- 

 paratively flat, and probably was never much more convex than it 



^ Trans. Geol. Soc. ser. 2, vol. i, pt. ii (1824) p. 395, pis. xl & xli. 



