228 PROP. H. Gr. SEELET ON ARISTOSTJCHUS PUSILLTTS. 



buted by Marsh to C<xlurus, and is similarly hollow. What is the 

 evidence of its association with the other remains cannot now be 

 determined. The bone has a well-marked basal canal, defined at 

 its extremity by the relatively large confluent facets for the chevron 

 bones, which, subtracting from the quadrate end of the bone, convert 

 it into a transversely ovate articulation. 



I conclude that this animal is distinct from every British Dinosaur, 

 but that it is nearly related to some imperfectly known types, de- 

 scribed by Prof. Marsh, like Allosaurus. But what the nature of 

 that relation may be must remain undetermined until more is known 

 of the American Dinosauria. 



EXPLANATION OF FIGURES. 



Plate XII. 



(The figures are of the natural size.) 



Fig. 13. Neural aspect of sacrum of Aristosuchus, showing the transverse pro- 

 cesses, metapophyses, and neural spines : ns, neural spine ; m, me- 

 tapophyses ; t, t, transverse processes ; pz, postzygapophysis. 

 14. Lateral view of sacrum and pubes, showing tneir association : /, fora- 

 men of sacral nerve ; p, pubic bones ; pz, postzygapophysis. 



Discussion. 



The President said that valuable work was being done by Prof. 

 Seeley in reexamining forms long since described, and comparing 

 them with the more recent American discoveries. 



Mr. Hflxe had known the specimen for a long time, even before 

 it was described by Prof. Owen. He quite agreed that the specimen 

 had nothing to do with Poikilopleuron. He thought the three ante- 

 rior vertebrae were different from the two posterior, and doubted if 

 the first three were sacral. The first transverse process appeared 

 to him longer than the others. The question as to whether the 

 remains were Crocodilian or Dinosaurian was intimately connected 

 with this identification of the vertebrae. There was also a question 

 as to whether the bones referred by Prof. Seeley to the pubis had 

 the form of symphysial union assigned to them. He preferred sus- 

 pending his judgment for the present. 



Prof. Seeley, in reply, said he thought if the specimen had been 

 before the Society there would not appear to be much difference be- 

 tween his views and Mr. Hulke's. He showed that the last vertebra 

 preserved was the posterior sacral vertebra because the posczygapophy- 

 ses were preserved, whilst the first three of the five had approximately 

 the same transverse measurement as the last two. Iso doubt the 

 transverse processes differ, but this is the case in other Dinosaurs. 

 It was quite possible that the pubic bones had the keel separately 

 ossified : but he thought there could be no doubt as to the osteo- 

 logical identification. 



