636 PROF. H. a. SEELEY ON THE SKULL OP 



may be some difficulty hereafter in determining the vertebral column 

 with which it was originally associated. 



Eirst it may be convenient to consider the upper surface of the 

 skull(Pl. XXY. fig. 1). The tenvporal fossce (TF) are large, ovate, and 

 narrower behind than in front, and have their posterior ends directed 

 a little outward and backward. Their length is about 6| inches, and 

 width about 3| inches. Their inner border is formed by the parietal 

 bones, the posterior border and posterior half of the lateral border by 

 the squamosal bone, and anterior border and anterior half of the 

 lateral border by the postfrontal bones. But on the inner side of 

 the outer bar above the eye is a plate of bone lapping along the inner 

 sides of the squamosal and postfrontal. The state of the specimen 

 does not demonstrate conclusively whether it is to be referred to 

 the squamosal or other postorbital element or to a separate bone not 

 hitherto recorded in the Ichthyosaurian skull. This outer margin 

 of the temporal fossa is comparatively straight ; the inner border is 

 much more curved. The outer bar, formed by the squamosal and 

 postfrontal bones, is thin, and on the whole suggests the same region 

 in the skull of Hatteria, though the squamosal bone extends further 

 forward on the outer side than in that living type. The extreme 

 width of the temporal fossae from one temporal bar to the other is 

 10 inches measured from the inner side, and about 11 inches 

 measured from the outer side. 



The supraoccipital bone is absent from the skull ; but since the 

 parietal terminates posteriorly in a suture in the shape of a broad 

 W with the median process less developed than the lateral wings, 

 which are prolonged outward and backward to meet the squamosal 

 bone, it is probable that it was fairly weU developed, and gave to 

 the back of the skull a transversely concave, but more than usually 

 straight transverse outline. The -parietal hones (p) are divided in the 

 middle line by a suture and are deeply grooved in the anterior part by 

 the fissure which terminates anteriorly in the parietal foramen (FP), 

 though this foramen is not more than 1^ inch wide, and the groove 

 is not more than 2| inches long, so that it is relatively much less 

 developed than in the Ichthyosaurs from the Lower Oolites. The 

 extreme length of the parietals is about 6| inches ; but in front 

 of the foramen the bones divide, and receive the narrow frontal 

 bones (/) between them for a length of about 2^ inches. The an- 

 terior divergences terminate in sharp-pointed processes which are 

 about 1^-Q inch apart. The parietal has its lateral surfaces, which 

 form the outer wall of the brain-case, smooth, concave in length, and 

 gently convex from above downward, so that the convex surfaces 

 form a slight median ridge above, except that the bone becomes a 

 little flattened laterally in front on each side of the parietal groove. 

 The least width of the bones in the middle of the brain- case is Cl- 

 inches. They widen posteriorly in a curve to 4^ inches. They also 

 widen anteriorly and send similar anterior processes along the an- 

 terior border of the postfrontal, and there the transverse expansion 

 is somewhat greater. These anterior lateral outlines of the parietal 

 bones are separated from the anterior forked terminations by the 



