PEOF. H. G. 3EELEY ON AEISTOSECHUS PUSILLUS. 



221 



20. Oil Aeistosuchus pusillus (Owen), being Fueihee Xotes on the 

 Fossils described by Sir R. Owen as Poieilopleueon pusillus, 

 Owen. By H. G. Seelet, F.R.S., F.G.S., Professor of Geo- 

 graphy in King's College, London. (Read March 9, 1887.) 



[Plate XII.] 



The Palaeontographical Society in 1876 published a memoir upon a 

 Wealden fossil, which Sir Richard Owen described as Poikilopleuron 

 pusillus. These bones were then in the collection of the Rev. W. 

 Darwin Pox, and, with the exception of the figured dorsal and 

 caudal vertebrae, subsequently passed into the British Museum, with 

 the Fox Collection. By the kindness of Dr. Henry Woodward, 

 F.R.S., Keeper of the Geological Department, I have been able to 

 examine these remains, and I would express my indebtedness for 

 the facilities given me in making the study of which the results 

 follow. 



A question necessarily arises as to the grounds on which the animal 

 is referred to the genus Poikilopleuron ^recte Pcecilopleurum), because 

 these are stated to be ;1 the shape and texture of the vertebrae, and 

 especially the latter.'*' This statement implies that when a dorsal ver- 

 tebra was divided vertically and longitudinally, it was found to have a 

 medullary cavity, comparable to that seen in the vertebrae of Poikilo- 

 pleuron. In the caudal vertebra the cavity is larger. Dr. Leidy, who 

 has recorded a vertebra of the Poikilopleuro '<-type in the Cretaceous 

 rocks of Colorado, remarks^trratan internal cavity of like character 

 was only known to him in the caudal vertebrae of the Ox ; but it is 

 probably not rare among Dinosaurian reptiles. Mr. Hulke has shown 

 that the character is also found in Megalosaurus, and other genera 

 with hollow vertebrae have been described by Profs. Marsh and 

 Cope. "Whatever the value of this character may be, I submit that 

 it is not generic, while there is no evidence which would associate 

 any group of osteological characters with chambered vertebrae 

 of this type. 



Mr. Hulke has advanced some evidence to show that Poikilo- 

 pleuron is Megalosaurus. and it will be admitted that the corre- 

 spondence in form and character of the caudal vertebrae, and in the 

 distal end of the tibia in these Oolitic Dinosaurs, if insufficient to 

 establish absolute identity, at least proves a close affinity between 

 them. And therefore the conclusion is legitimate that the re- 

 semblances found in the tail extend substantially to the sacrum, and 

 that the same type of sacrum is found in Poikilopleuron as in ILega- 

 losaurus. When examining the validity of the genus Poikilopleuron 

 Mr. Hulke did not discuss the sacrum, which constitutes the chief 

 part of the evidence for the species Poikilopleuron pusillus. 



If Sir Richard Owen is correct in his description of the sacrum of 

 that fossil in referring only two vertebrae to the sacral region, and 

 if the sacrum of Megalosaurus consists of five anchylosed vertebrae, 



