436 PROF. T, H. HUXLEY ON STAGONOLEPIS KOBEKTSONI, 



of Lizards only in the somewhat greater size and lower position of 

 the inner trochanter of the femur, and in the large cnemial end of 

 the tibia, bnt devoid of the special peculiarities observed in the 

 ankle-joint of the typical Ornithoscelida. We unfortunately know 

 nothing of the structure of the ventral elements of the pelvis. The 

 ilium, as has been seen, is Lacertilian in form, Ornithoscelidan in 

 the character of the acetabulum. But the vertebrae and the implan- 

 tation of the teeth are, as in the typical Ornithoscelida, Crocodilian, 

 and not Lacertilian. 



Such evidence as the imperfect materials at present extant offer 

 tends to show that the Triassic Thecodontosauria were devoid of 

 some of the most marked peculiarities of the later Ornithoscelida ; 

 while, on the other hand, the most ornithic of Ornithoscelida at 

 present known, such as Iguanodon, Hadrosaurus, Hypsilophodon, and 

 Lcelaps, belong to the later half of the Mesozoic period. 



Just as the oldest Crocodiles differ less from the Lacertilia than 

 the recent Crocodiles do, so it appears that the oldest Ornithoscelida 

 approached a less differentiated Lacertilian form. The Crocodilia 

 and the Ornithoscelida appear to converge towards the common 

 form of a Lizard with Crocodilian vertebrae. 



On the evidence of such remains of Cetiosaurus as had come to 

 light in 1869 I have assigned a place among the Dinosauria to that 

 reptile. The materials subsequently brought together and described 

 by the late Prof. Phillips do not, however, bear out this view, but 

 show that Cetiosaurus is, like a Thecodontosaurian, a reptile with 

 a vertebral system similar to that of the Ornithoscelida and Croco- 

 dilia, but with more Lacertilian limbs ; and it may be that Steno- 

 pelyx is in the same predicament. If further information confirms 

 this suspicion, it will probably be convenient to separate the Theco- 

 dontosauria, Cetiosaurus, and perhaps Stenopelyx, as a group of the 

 Suchospondylia, distinct from the Ornithoscelida on the one hand, and 

 the Crocodilia on the other, under the name of " Sauroscelida." 



EXPLANATION OF PLATE XIX. 



View of the palatine face of the posterior half of the skull in one Eusuchian 

 and three Mesosuchian Crocodiles, showing the modifications in the form and 

 position of the secondary posterior nares. 



Fig. 1. Steneosaurus Larteti. (Deslongchamps, " Notes Paleontologiques," pi. 

 xiv. fig. 2.) 



2. Metriorhynchus Blainvillii. (Deslongchamps, ibid. pi. xx. fig. lb.) 



3. The Crocodilian skull from the Wealden at Brook Point, in the Isle of 



Wight. Of the natural size. 



4. G-avialis gangeticus. (D'Alton and Burmeister, 'Der fossile Gavial 



von Boll/ pi. iv. fig. 2.) 



Discussion-. 



Prof. Duncan" said that it was impossible to criticise a paper of 

 this kind, and that it would perhaps be a greater compliment to 

 give a silent assent to the author's statements. At the same time 



