AN ICHTHYOSAURtJS PROM THE LIAS OF WHITBY. 645 



There now only remain on the palate the articular ends of the 

 laro^e quadrate hones (q). These extend below the level of the palate 

 and are subreniform, concave on the inner border where the ptery- 

 goid abuts, convex on the outer border, and narrower in front than 

 behind. The articular surfaces are arranged longitudinally, and 

 are more than twice as long as wide, convex in length as well as 

 from side to side. That on the left side is a good deal broken 

 away. The length of the articular surface is about 3^ inches, 

 while its width did not exceed IJ inch. 



I have already compared the skull of Ichthyosaurus with that of 

 other extinct and living animals, in a paper published by the Linnean 

 Society in February 1876 (Journal, vol. xii. p. 296), and only here 

 would draw attention to the view enunciated by Professor Owen in 

 the report of his lecture at the School of Mines in 1858 (Ann. Nat. 

 Hist. ser. 3, vol. i. p. 395), that a truer conception of the affinities of 

 the Ichthyosaurus may be obtained by comparison with Labyrintho- 

 donts and other Triassic reptiles than with modern Lacertians and 

 Crocodilians, for the sake of showing that the Crocodilian characters 

 of the skull have been somewhat underestimated. In the memoir 

 referred to I merely stated facts and possible interpretations. Now 

 it seems to me that we are justified in going a step further, and by 

 comparison with the Teleosaurs may gain some better insight into 

 the relation of Ichthyosaurs with Crocodiles than would be furnished 

 merely by evidence from the existence of bony elements like the 

 supraquadrate bone only elsewhere found among Labyrinthodonts. 

 For in the Teleosaurian genera we see the palate in process of being 

 closed in the median line, though it is still open ; and if the maxil- 

 lary bones of Ichthyosaurus were supposed to develop larger palatine 

 plates, so as to close the palate in the median line, then the palatine 

 bones would come together as in the Crocodiles, and the pterygoid 

 bones would be overlapped by them in part according to the Cro- 

 codilian pattern. If the median vacuities in the Ichthyosaurian 

 skull were closed by the pterygoids meeting, then the vacuities 

 between the transverse and palatine bones would remain homolo- 

 gous with the large palatal vacuities of Crocodiles, and the cavity 

 behind the transverse bone in Crocodiles would correspond to the 

 similar cavity in Ichthyosaurus, The Ichthyosaurian palate there- 

 fore seems to me to represent the Crocodilian palate before it has 

 made any approximation to the median closing of the bones, which 

 is one of the characteristics of the existing order. 



With regard to the upper surface of the skull, both postorbital 

 and supraquadrate bones are clearly unossified in the recent type ; 

 but the vacuities exist in Crocodiles in which they should be de- 

 veloped. The most striking differences of the hinder part of the 

 skull in the two orders are chiefly matters of proportion, consequent 

 upon the reduced size of the orbits in Crocodiles and their consequent 

 loss of a more or less vertical position. But in fossil Crocodiles and 

 Teleosaurs the temporal fossse are relatively larger than in the living 

 form ; and in these animals we find a small prelachrymal vacuity 

 which occupies the position of the external nasal openings in Ich- 



