﻿WEALDEN FORMATIONS. 



7 



nervous source. The contrast in the relative size of the myelon and vertebra between 

 the Eagle and the Chondrosteosaur is shown by figs. 1 and 3, n, in Plate IV. 



The specimen here described and figured was obtained from the submerged Wealden 

 deposit on the south coast of the Isle of Wight, and was purchased for the British 

 Museum. 



Species. Chondrosteosaurus magnus, Ow. Plate VI. 

 Syn. BothriospondyJus magnus, Ow. 



A mutilated centrum from the same formation and locality as that of Chondrosteo- 

 saurus gigas has been kindly transmitted to me for the purpose of the present Monograph, 

 by its discoverer, the Rev. Wm. Fox, M.A. 



Sufficient of the concave articular surface is preserved to show its correspondence in 

 size with that of the foregoing vertebra, but its proportions are reversed, the vertical 

 diameter plainly appearing to surpass the transverse one. This vertebra, it is true, has 

 come from a more posterior part of the column. The parapophysis has disappeared, at 

 least from the position from which it projects in the subject of Plate II : if such process 

 was present its origin has risen to near the base of the neural arch. So much of the 

 free surface of the centrum as remains is concave lengthwise ; all trace of flattening of the 

 inferior surface has disappeared. The curve of the free surface toward the fore end of 

 the centrum indicates that vertebral element to have been shorter absolutely, and much 

 more so relatively to the hinder cup, than in Chondrosteosaurus gigas. It is hard 

 to suppose that so extreme a degree of modification of shape and proportion should be 

 present in an anterior and a middle dorsal vertebra of the same spine or in the same 

 species, as is exemplified by the subjects of Plates III and VI ; I therefore refer 

 them, provisionally, to distinct species. The present vertebra agrees more closely in 

 proportions with that of which a side view is given in a former Monograph. 1 



The extreme modification of structure in both that vertebra and the subjects of the 

 present Monograph lead me to refer them to a distinct genus from Bothriospondylus ; but 

 it is a nearly allied one. 



I had a vertical longitudinal section made of a rolled and worn centrum, of smaller 

 size than the type of Chondrosteosaurus gigas, but of similar proportions. It is figured 

 three fourths of the natural size in Plate V, fig. 2. The black tint indicates the 

 ossified proportion of the vertebral substance ; the lighter tint the chondrosal proportion, 

 filled in the fossil by Wealden marl. 



1 ' British Fossil Reptilia of the Mesozoic Formations,' Part II, PI. VIII, Pal. Soc. vol. for the year 18/5. 



