46 MAKLNE EEPTIF.ES OF THE OXEOED CLAY. 



errors lias already been published (Geol. Mag. [5] vol. viii. (1911) p. 160), but it, 

 nevertheless, seems advisable to repeat the correction in the present volume, and this 

 will be done below. 



In Peloneustes the mandible (text-fig. 14, A, B) is composed of the following 

 elements: (1) the united surangular and articular ; (2) the angular; (3) the dentary ; 

 (4) the coronoid ; (5) the splenial. Of these, as usual, the dentary (d.) is much the 

 largest ; this bone unites in front with its fellow of the opposite side in a long 

 symphysis, in the posterior part of which, however, the two are separated ventrally by 

 the splenials, which there unite with one another ; it appears also that the deutal 

 canals are prolonged for some distance into the symphysis ; the anterior ends of the 

 coronoids (cor., text-fig. 14) also extend just into the hinder portion of the upper 

 part of the symphysis, though they do not seem to have actually united with one 

 another. The upper surface of the dentary symphysis (d.sgm.) is raised in the middle 

 line into a strong ridge, which is separated from the alveoli on each side by a deep 

 groove, at the bottom of which the tips of the replacing teeth appear. The symphysis, 

 as a whole, is a little expanded, being widest opposite the fifth and sixth teeth, which 

 are enlarged ; towards its hinder end the teeth become smaller and the symphysis 

 narrows considerably. In Peloneustes philarchus there are 14-16 teeth in the 

 symphysis, while in P. evansi the number is only twelve. The outer surface of the 

 dentaries is gently convex from above downwards, and is marked by a number of short 

 grooves terminating in vascular foramina, at least in the upper half. On the iuner 

 face there is a deep longitudinal dental groove, which, as above mentioned, extends 

 into the symphysial region. Behind this the channel is closed on the inner side by 

 the coronoid (cor.) above and the splenial (spl.) below ; at its posterior end it opens 

 just behind the level of the coronoid process, the aperture (g.) being bounded by the 

 surangular (s.ang.art.) externally and the splenial (spl.) on the inner side. The 

 floor of the groove in its posterior portion is formed by the forward prolongation of 

 the angular (ang.), which extends beneath ihe splenial and dentary and forms the 

 lower border of the mandibular ramus to within a few centimetres of the symphysis. 

 At its posterior end the dentary rises to the coronoid angle and overlaps the outer 

 face of the surangular above and of the angular below. The alveolar border of the 

 portion of the dentary behind the symphysis bears alveoli for about twenty-five teeth, 

 the posterior ones being very small ; on the inner side of the alveoli there is a groove, 

 at the bottom of which the tips of the replacing teeth appear. 



The coronoid (cor.) is in several respects remarkable ; it is a large bone extending 

 from the coronoid angle, which it helps to form, to just within the symphysis, where 

 it is in contact with its fellow of the opposite side, but probably does not actually 

 unite with it. At its hinder end it unites with the surangular in an almost vertical 

 suture, and throughout its length it is closely applied to the inner face of the dentary, 

 its upper edge being close to and nearly parallel with the alveolar border of that bone. 



