ON THE SSULL OF AN ICHTilTOSATJEtrS, 635 



45. On the Skull of an Ichthyosaukus from the Lias of Whitby, 

 apparently indicating a new Species (I. Zetlandicits, Seeley), 

 preserved in the Woodwardian Museum of the IJniveesity oe 

 Cambridge. By Professor H. G. Seeley, F.E.S., E.G.S., &c. 

 (Eead June 23, 1880.) 



[Plate XXV.] 



Earl Zetland many years ago presented to the Woodwardian 

 Museum a superb skull of Ichthyosaurus^ which pertains to a new 

 species, and from its value in exemplifying the osteology of the 

 skull is in many respects the finest specimen known. 



The anterior part of the snout is lost, but what remains of the 

 head is 28 inches long. The snout has the aspect of having been at 

 least 6 inches longer. Where fractured in front the jaw is 3 inches 

 wide and 2| inches deep. Its greatest transverse width behind the 

 eyes and in front of the quadrate bones is 16| inches, so that it 

 would appear to have been somewhat more than twice as long as 

 wide. The occipital region unfortunately is badly preserved, and 

 the basioccipital bone is a little displaced downward and forward. 

 There is also some imperfection of the bones of the right orbit ; but 

 otherwise the skull is in excellent preservation. Being in a hard 

 limestone it has escaped compression and distortion, and the lime- 

 stone having been cleared with a chisel, the bones of the palate 

 as well as those of the upper surface of the skull are beautifully 

 displayed. 



In transverse section behind, the outline is a trapezoid; the 

 upper outline of the skull, being flat and horizontal, is 10 inches 

 wide and parallel to the lower outline. The base, as already 

 mentioned, is 16| inches wide. The oblique sides formed by the 

 bones behind the orbits are 7| inches from the base of the quad- 

 rato-jugal to the junction of the squamosal with the postfrontal. 

 From the middle of the orbit backward the lateral outline is convex, 

 and though the margin of the orbit is nearly straight the lateral 

 outline anterior to it is gently concave. The flattening of the skull 

 on its upper part covers a triangular space defined by rounded 

 angular ridges crossing the nasal bones, and converging forward to 

 disappear in their anterior third. These ridges, prolonged backward, 

 cross the postfrontal and become prolonged round the outer and 

 upper border of the temporal fossae. External to this space, which is 

 depressed and concave in the region of the nasal and frontal bones, 

 are the sloping sides of the skull, which converge upward, and in the 

 anterior part of the snout, formed by the premaxillary and nasal bones, 

 round together into a somewhat semicylindrical form. Posterior 

 to the orbit there is a convergence of the lateral areas towards the 

 occipital region. This broad flattened form of a skull with oblique 

 orbits looking upward and outward is so different from all European 

 species hitherto figured that I venture to describe it, although there 



