Oeological Society. 135 



port the lower lobe. The neurapophyses extend from the occipital 

 region of the skull to the base of the dorsal fin, 13 inches. In this 

 length there are preserved thirty-five neurapophyses, representing 

 the same number of vertebrae. The first ray of the dorsal fin is 

 inserted above the thirtieth vertebra ; the total number of vertebra 

 in the spinal column would be from eighty to eighty-five. The 

 caudal fin is very large and was a powerful organ of propulsion ; its 

 upper lobe, as in the recent Sturgeon, is the longer of the two. 



The specimen is nearly twice the length of those described by 

 Egerton, and the Author indicated the differences in some detail. 

 The division of the scapular arch into three parts, the suprascapula, 

 the scapula, and the coracoid, appears to be undoubted, whilst in the 

 specimens previously described the scapula and coracoid are said to 

 be united. The two latter ossifications of the shoulder-girdle are 

 separate in the existing Sturgeons, and in the Ganoid fishes this ia 

 also generally the case. 



The Author then referred to the opinion expressed by Sir P. Eger- 

 ton as to the homology of the cranial plates of fossil Sturgeons when 

 compared with recent ones and also with Teleosteans, and to the 

 confirmation of these views by Prof. Parker, who concludes that, 

 although the Sturgeons cannot be said to occupy an intermediate 

 position directly between the Selachians and the Bony Ganoids, yet 

 on the whole that is their position. 



Lastly, the Author states his belief that there is no specific differ- 

 ence between O. acipenseroides, Agassiz, and G. crassior, Egerton. 



2. " On Aristosuchus pv^sillus, Ow., being further Notes on the 

 Fossils described by Sir R. Owen as Poikilopleuron pusillus, Ow." 

 By Prof. H. 0. Seeley, F.R.S., E.G.S. 



A AVealden fossil, comprising certain dorsal, sacral, and caudal 

 vertebrae, with some associated bones belonging to the pubic region, 

 formerly in the collection of the Rev. W. Darwin Fox, but now in 

 the British Museum, was described by Sir R. Owen in 1876 as 

 PoiTcilopleuron pusillus. In the present paper the author showed 

 that the presence of a peculiarly shaped medullary cavity in certain 

 vertebrae, a character upon the strength of which the bones were 

 referred to PoikilopTeuron, Desk, was not peculiar to that genus, but 

 had been found in Megalosaurus and in other Dinosaurian reptiles, 

 whilst the characters of the sacrum in " Poikilopleuron pusillus " 

 differed from those of any Crocodilia. The species was clearly not a 

 Poikilopleuron, but was apparently a Dinosaur belonging to an un- 

 described genus, for which the name of Aristosuchus was proposed. 



The pubic bones were described and shown to resemble those 

 noticed by Prof. Marsh in Allosaurus, Ceratosaurus, and Goelurus, 

 and the specimen itself has been referred by Prof. Marsh to the last- 

 named genus. The genera named were, however, placed in dis- 

 tinct Dinosaurian suborders, and consequently it was evident that 

 the pubic bones by themselves were insufficient for generic determi- 

 nation, whilst the dorsal vertebra of the Wealden fossil had the 



