METEIOEHTNCHUS. 



145 



the sides being concealed and the thin bones of the palate destroyed. Besides 

 making it difficult to work out the structure of the skull, this crushing also renders 

 the measurements, particularly those of width, very unreliable. 



In its general outline (text-fig. 55) the skull seen from above is an elongated 

 isosceles triangle ; the height of the triangle (i. e. the length of the skull) differs much 

 in its relative proportion to the base (i. e. the width between the outer angle of the 

 quadrates) in the various species, the difference in length depending mainly on 

 the degree of development of the rostral (preorbital) region. The premaxillary region 

 is pointed and shows no expansion such as occurs in the Steneosaurs. The posterior 

 (occipital) surface of the skull is triangular in outline and is by no means so depressed 

 as in Steneosaurus, but unfortunately in nearly all cases it is greatly deformed by 

 crushing. The large temporal fossas vary somewhat in form and size in the different 



Text-fig. 55. 



nar. fljnx. 



r & 



Semi-diagrammatic view of skull of Metriorhynchus superciliosum, from above. 

 ale., alisphenoid ; hoc, basioccipital ; e.v.o., exoccipital ; /., frontal ; for., foramen in hinder wall of temporal 

 fossa ; j., jugal ; tw, maxilla ; n., nasal ; nar., external nares ; orb., orbit ; par., parietal ; prn.v., 

 premaxilla ; po.f., postfrontal ; pr.f., prefrontal ; pr.o., pro-otic ; q., quadrate ; §.?'., quadrato-jugal ; 

 sq., squamosal. 



species, but may be said to be roughly quadrangular with the angles rounded off to a 

 varying extent. 



The premaxill(B {pmcc.) form the anterior extremity of the pointed snout. Above, 

 they surround the external narial aperture, which is usually an elongated heart- 

 shaped opening, the indentation on its posterior border being formed by a pair of 

 processes of the premaxillae projecting forwards. In Geosaurus, according to Fraas*, 

 these processes completely divide the nasal opening in the middle line, but. this is not 



* Palteontographica, vol. xlix. (1902) p. 43. 



PART II. 



U 



