﻿Vol. 64.] JBRACHYRHYNCHUS FEOM THE OXFORD CLAY. 349 



given by Deslongchamps, as he supposes all the Metriorhynchidae 

 to have had between 50 and 56 teeth in the upper jaws, and 

 ascribes the error to the imperfection of the skn]l ; but a reference 

 to Deslongchamps's figure will show that, considering the size of 

 the alveoli, it would be impossible to add more than two or three 

 teeth to the maxilla, and the skulls in the Eyebury Collection bear 

 out fully the undoubted correctness of his estimate. Only a few 

 imperfect teeth are preserved ; they do not differ noticeably from 

 those of M. superciliosus. 



Nasals. — Considering the great distance by which the nasals 

 encroach on the median line, it is surprising to find that they agree 

 in length along that line with two skulls of If. superciliosus, in which 

 there is an interval of 60 and 70 millimetres between the nasals and 

 the prsemaxillse ; but they are, of course, much longer along their 

 exterior border as they widen out more rapidly, attaining a width 

 of 160 mm., and more at the point of the prsefrontals. They are 

 almost smooth anteriorly, but are marked with slight grooves in the 

 median ramus of their posterior end, the portion outside the prse- 

 frontals being sculptured with long sharp ridges. 



Frontal region. — The frontal bone is greatly developed in 

 this species, exceeding that of M. superciliosus by some 35 to 50 mm. 

 in length and 10 to 25 mm. in breadth, taken across the narrow 

 part of the orbits. In No. 164 the frontal is 200 mm. long and 

 105 mm. wide, in No. 165 it is 185 mm. long and 115 mm. wide ; 

 while a skull of M. superciliosus of average length (655 mm.) 

 shows a length of 150 and a width of 94 mm. It is the great 

 development of the frontal and praefrontals that helps to impart so 

 massive an appearance to the skull. 



The prsefrontals are enormous, being 115 mm. long and 

 80 mm. broad, as compared with 90 and 55 mm. respectively in 

 M. superciliosus. The deflex processes of the bones on their inner 

 surface are also very robust. Deslongchamps writes concerning the 

 prsefrontals (op. jam cit. pp. 337-38) : — 



' dans le genre Metriorhynque, c'est I'espece on ce frontal anterieur occupe le 

 phis d'espace dans le contour de Torbite.' 



The suture of the frontal and prsefrontal commences at the centre 

 of the interior border of the orbit, and the posterior border of the 

 prsefrontal from that point to its exterior corner measures some 

 70 mm. in length ; for, instead of the curved exterior border which 

 we find in M. superciliosus, this border in M. bracliyrhynclius is 

 practically at right angles to the exterior margin of the skull. 



It has just been stated that the suture of the frontal and praefrontal 

 commences at the centre of the interior border of the orbit. Not 

 only is this the case, but it forms almost a continuous line with 

 the curve of the postfrontal right up the point of the frontal, except 

 for a slight deviation, where the posterior point of the nasal sepa- 

 rates the pra)frontal from the point of the frontal. 



