﻿356 ME. E. THURLOTV LEEDS OX 2IETBI0BHYXCHUS [Aug. I908, 



The pterygoids are slightly crushed out of their original posi- 

 tion, and, owing to fracture, their relations with the basis cranii 

 are obscure. Posteriorly the pterygoids united, and show a tuberosit}- 

 on each side of their median line. Anterior to this they curved 

 upwards and outwards, to form the roof of the posterior nares ; they 

 are then separated by the point of the vomerine, as I have already 

 remarked. At their exterior border the pterygoids, which poste- 

 riorly have a thickened edge, widen out rapidh* to form the lateral 

 ramus that joined the transverse bone : this bone is unfortu- 

 nately missing. Anterior to the main lateral ramus is a second 

 and more slender one, after which the bone forms a curve and runs 

 forward almost to a point, becoming very thin. The lateral ramus 

 had a slight upward curve to form the transpalatine arcade ; its 

 posterior border is thick, its outer edge thin, while the anterior 

 horder presents a roughened surface right into the notch, between 

 it and the second ramus, with which surface the transverse bone had 

 sutural connexion. On the exterior surface of the pterygoids there 

 is a marked depression, into which the outer ramus of the palatines 

 fitted. 



To sum up, we find in the Eyebury specimens the characteristics 

 determining Deslongchamps's species, although the praefrontals, 

 which are in keeping with the general massive development of the 

 skull, are wider than he supposed; and we are able to recon- 

 struct with almost absolute certainty the region of the posterior 

 nares, showing the bifurcated opening with the vomerine element 

 running back almost to the sphenoid — a feature which I think future 

 research and discoveries will prove to be common to aU the 

 Aletriorhynchidae. 



In conclusion, I wish to express my gratitude to Dr. C. W. 

 Andrews, F.E.S., for much kind assistance rendered to me while 

 working at the British Museum (2^atural History), and also to 

 acknowledge several valuable suggestions made by him. 



EXPLANATION OF PLATES XL & XLL 

 [The figures are about oue-sixth of the natural size.] 



Plate XL. 



TTpper aspect of skulls of Metriorhynchus hrouchyrhynchus (DesL), 

 Nos. 164 & 165 (Leeds Catal.). 



Plate XLL 

 Palatal aspect of the same. 



