234 Reports and Proceedings — 



from existing species; there is no evidence of teeth. Prom the 

 position of the respective maxillary and premaxillary bones in this 

 specimen there can be no further doubt that the small bifurcated bone 

 of C. acipenseroides, Ag., described as the maxillary bone, is really the 

 premaxillary. 



Bony neurapophyses are preserved in the anterior portion of the 

 body. There is no trace of the vertebral column nor of ribs or 

 hsemapophyses, except in the caudal fin, where hsemapophyses support 

 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 vertebrae 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 indicates 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 is 

 also generally the case. 



The author then refers to the opinion expressed by Sir P. Egerton 

 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 

 difference between C. acipenseroides, Agassiz, and C. crassior, Egerton. 



2. " On Aristosuchus pusilliis, Ow., being further Notes on the 

 Possils described by Sir R. Owen as Poihilopleuron pusillus, Ow." By 

 Prof. H. G. Seeley, P.R.S., F.G.S. 



A Wealden fossil, comprising certain dorsal, sacral and caudal 

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

 formei'ly in the collection of the Pev. W. Darwin Pox, but now in 

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

 Poihilopleuron 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 Poikilopleuron, DesL, 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. March in Allosaurus, Ceratosaurus, and Coelurus, and 



