464 



and had a somewhat radiated arrangement from the centre to the 

 cu'cumference. While in others, two of these modes were united in 

 strengthening the osseous cups. 



The peculiarities of these double osseous cups, and their supporting 

 columns, were pointed out in the vertebrae of the Common Skate 

 (Raia batis), Thornback Ray (R. clavata), Sharp-nosed Ray (R. 

 oxyrhynchus), Starry Ray (R. radiata), Common Dog-fish (Scyllium 

 Catulus), Spotted Dogfish (S. canicula), Picked Dog-fish (Spinax 

 acanthias), Common Tope (Galeus vulgaris), Basking Shark (Selache 

 maximus), White Shark (Carcharias vulgaris). Saw-fish (Pristis 

 antiquorum), and Chimsera (Chimsera monstrosa). 



The vertebral column of the Sturiones and Cyclostomi was shewn 

 to be essentially composed of soft transparent cartilage. 



It was demonstrated by a chemical analysis of the essential osseous 

 portions of the vertebrtc, that they were true bone. This was evi- 

 denced by their containing the same amount of earthy and animal 

 matters, as the bones of osseous fishes, as well as by their earthy 

 salts being of the same nature in both classes of bones. The result 

 of the author's analysis gives, as a mean, about 69 per cent, of earthy 

 matters, chiefly consisting of phosphate of lime, and 31 per cent, of 

 cartilage. The chemical composition of the common cartilaginous 

 skeleton, and of the vertebrae, with their encrusting cartilage and 

 calcai'eous granules, was also noticed, in order to shew the essential 

 difference between them and the truly osseous portion of the ver- 

 tebrae. 



From these peculiarities in the spinal column of the Plagiostomi 

 (Rays and Sharks), taken in connection with the higher degree of 

 development of their nervous, genei'ative, and digestive systems, the 

 author concluded, that these fishes ought to form a new sub- 

 class, and, in the descending scale of organization, be placed at the 

 head of the fishes, as they manifestly form the connecting link be- 

 tween the osseous fishes and the reptiles. He also concluded, that 

 the Sturiones and Cyclostomi ought to be arranged together as a 

 distinct subclass, to which the term of cartilaginous might still be I'e- 

 tained, and be placed after the osseous fishes, in the descending scale 

 of natural classification ; as the lower grade of development of their 

 whole systems, taken along with their essentially cartilaginous skele- 

 tons, constituted them the connecting link between the higher mol- 

 lusca and the more imperfectly oi'ganized osseous fishes. 



The paper was concluded by pointing out the probable importance 



