250 MEMOlJUi or THE (Jl' IJKXSLAXl) MFSKUM. 



lost in matrix. The pterygoids provide tlie greater part of the base of the posterior 

 moiety of the skull. On the left-hand side the pterygoid is in juxtaposition with 

 and somewhat overlaps, owing to displacement, the basioccipital and basisphencid. 

 The right pterygoid' has been tilted })elow the plane of the flanges presented by the 

 axial bones. From th? basi )3cipital to the lateral border the pterygoid attains a 

 maximum breadth of 110 mm. 



Owing to the presence of superimposed hyoid rods, and a brecciated mass 

 of broken teeth and matrix containin.g associated fossils, the central portion of the 

 lower surface of the fossil is obscured. The extent of the interpterygoid vacuities 

 cannot be gauged, but. judging from the converging inner margins of the bones, 

 the contours in this area are similar to tlie skull of Ichthyosaurus longifrons as 

 figured by Owen.' The palatine elements appear to be displaced and are not vi&ible 

 in the same plane. 



Posterior Region. — The contours of the sii*:>erior border of the occipital 

 region, formed by the parietals and processes from the squamosals, are quite 

 continuous, being convex in the median area and then sloping to lateral concavities. 

 Viewed from above, the postero-external borders of the squamosal are seen to 

 curve syminetrically backwards, and, although the occiput is somewhat disrupted, 

 the contours are quite elegant. The inner process of the squamosal unites in an 

 oblique suture with the lateral arm of the parietal near the median line of the 

 supratemporal fossa. 



A large quadrate is present on each side, but owing to mandibular pressure 

 these bones have been forced somewhat out of position. 



Above the region of the foramen magnum, only small fragments are visible 

 in the matrix of elements which correspond to the superior occipitaha, which have 

 apparently been forced inwards. Possibly these are paired extensions of the 

 supraoccipital which form part of the lateral borders of the foramen magnum. 



The opisthotics are in place on each side, and junction with the basioccipital, 

 the " stapes," and the squamosal. 



SUOGE.STIONS FOR A Re-INTERPRETATION OF THE SO-CALLED StaPES — 



Next to the quadrate, the largest bone in the occipital region is the element 

 called "stapes" by Sollas and Andrews. This acts as a strong lateral buttress of 

 the basioccipital, and lies above the posterior flange of the pterygoid. It has an 

 expanded facet for junction with the basioccipital, with an adjoining superior 

 surface for association with the opisthotic. Cope,^ who was the first to name this 

 bone, did so with diffidence, and figured it as distinctly separated from the basi- 

 CK'cipital, whereas modern authors rightly show it as a buttress supporting the 

 rostrum of the condyle. Owen^ named it the paroccipital, but apparently only 



'Owen, Liassic Reptilia, Mon. Pal. Soc, 1881, PI. XXV. 

 ^Cope, Proc. Amer. Assn. Ad. Sc, 1871, p. 199, fig. 2. 

 * Owen, Mon. loc. ct., p. 94. 



