WEALDEN FORMATIONS. 25 



vertebrae from the coast at Brook Point, Isle of Wight, which, among the bones of 

 Iguanodon and other gigantic Wealden genera, contains the centrum or body of a 

 dorsal vertebra of the great Streptospondi/lus. This specimen, though much rolled 

 and worn, is interesting, inasmuch as it exhibits the characteristic contraction of the 

 middle and expansion of the ends of the centrum, together with unequivocal evidences 

 of the marked depression on each side, near the upper part of the anterior or convex 

 end of the centrum. What remains of the depression is about the size of the end of a 

 man's thumb. The convexity of the anterior extremity resembles in degree, and 

 likewise in irregularity, that in the fractured vertebra of the Streptospondylus from the 

 lower Oolite, in Mr. Kingdon's collection. 



The present centrum is less depressed than those of the cervical region, but agrees 

 with them in length, as the following dimensions show : 



Tncli. Lines. 

 Antero-posterior diameter . . . . . . 5* 



Vertical diameter of concave end . . . . . .56 



Transverse diameter of concave end . . . . .53 



Transverse diameter of middle of centrum . . . .30 



In Tab. V, tig. 4, a reduced figure of two of the anterior (cervical ?) vertebrae of 

 the young Iguanodon from Cowleaze Chine, is reproduced to show the difference in the 

 form of the angle between the ridges diverging from the neural spine to the posterior 

 zygapophyses, and in the form of the ridges themselves, which are much sharper in 

 Iguanodon than in Streptospondylus major ; the degree of the terminal convexity and 

 concavity of the centrum are both less marked in the Iguanodon. 



Dorsal vertebra of Streptospondylus major. Tab. VII. 



I am now able to carry out the comparison of the Iguanodont and large Wealden 

 Streptospondylian vertebrae at the part of the dorsal region where the parapophysis 

 has passed from the centrum to the neural arch, and this is decisive against the 

 ascription of the latter vertebrae to the Iguanodon. 



That the dorsal vertebra, with a convexo-concave centrum, belongs to the same 

 species as the cervical vertebrae here described and referred to Streptospondylus major, 

 is shown by the same vertical contour of the sides of the centrum, convex at the upper 

 and concave at the lower half, and by the shape of the thick, obtusely rounded, inferior 

 median ridge, which still shows the triangular form with the posterior base, and is 

 slightly convex lengthwise (Tab. VII, fig. 3). In the corfesponding vertebra of the 

 Iguanodon the upper half of the side of the centrum is slightly concave vertically, and 



"' The margins of the extremities being worn and rounded prevent the actual length being given. 



