204 Dr. C. W. Andrews—An Ichthyosaur from Peterborough. 
facets of the quadrates; below they lie in a groove on the upper 
surface of the pterygoids (pt.), the postero-external wings of which 
also unite firmly with the inner surface of the quadrates. These 
tones are further supported above by the squamosals (q¢.b.sq.), which 
closely embrace tneir upper ends and send down their inner faces 
processes which overlap the ascending processes of the pterygoids. 
The squamosals themselves are further supported by the outer ends of 
Fig. 2.—-Ophthaimosaurus icenicus, Seeley. Reconstruction of the posterior surface 
of skull. About 4 nat. size. 
art. articular surface of quadrate ; boc. basi-oceipital ; cond. occipital condyle ; 
exo. exoccipital ; for. foramen in supra-occipital; for. mag. foramen magnum ; 
op. opisthotic ; op.f. facet for opisthotic ; py. process of supra-occipital projecting 
into foramen magnum; pa.f. facet for parietal; p.d.sq. parietal branch of 
squamosal; p.e.a. postero-external angle of squamosal; pt. pterygoid; pt.foss. 
post-temporal fossa; g. quadrate; g.d.sqg. quadrate branch of squamosal ; 
g.j- quadratojugal; soc. supra-occipital; s¢. stapes: ¢.0.sg. temporal branch 
of squamosal ; x11, foramen for posterior branch of the hypoglossal nerve. 
the opisthotics (op.), which internally rest upon the basi-occipital 
and the exoccipitals. The supra-occipital (soc.) consists of a lateral 
epiotic region, which is impressed by two of the semicircular canals, 
and a posterior occipital region, which is perforated on either side 
of the middle line by a large foramen (/for.), which may have 
transmitted a blood-vessel or may possibly have something to do with 
the peculiarly modified auditory apparatus, and have served for the 
passage of an enlarged ductus endolymphaticus. 
The other parts of the skull do not present any peculiarities of 
sufficient importance to be noticed here. ‘The sclerotic ring consists 
of about fourteen plates, which are united by suture and bend round 
on to the posterior surface of the eyeball, as was pointed out by 
Owen ' in Jchthyosaurus and recently by Gilmore * in Baptanodon. 
1 Foss. Rept. Liassic Form., pt. iii (Mon. Pal. Soc., 1881), p. 1038 
2 Mem. Carnegie Museum, vol. 1i (1906), p. 328. 
