WEALDEN FORMATIONS. 11 



specimen from Dry Sandford. The remaining vertebras in this specimen are 

 characterised by the same smooth and polished surface, rich brown colour, contraction 

 of the middle of the body, its cylindrical form transversely, and the longitudinal fossa 

 below the annular part, as in the Oxford specimen. The length of this series is one 

 foot six inches and a half ; the second and third sacral vertebrae are rather shorter 

 than the rest. The first sacral vertebra, which was not anchylosed to the last lumbar, 

 gives the following dimensions : — 



In. Lines. 



Anteroposterior diameter of centrum . . . . .5 



Vertical diameter of anterior articular end . . . . .4 



Transverse diameter of anterior articular end , . . .4 6 



The neural arch seems not to have been coextensive in length with the centrum, but 

 rests on its anterior three fourths. A strong and short parapophysis extends obliquely 

 upwards and backwards from each side of the arch ; the antero-posterior diameter of 

 the base of this process is two inches, its vertical diameter one inch and a half. In 

 the second sacral vertebra the neural arch has moved forward upon the interspace 

 between the first and second sacral bodies, and developes from the lower part of its 

 base a stronger, thicker, and longer parapophysis, directed outwards and forwards. 

 The third neural arch has its base transferred directly over the interspace of the second 

 and third centrums ; the diameters of the base of its parapophyses are three inches and 

 two and a half inches : they incline slightly backwards. The fourth neural arch 

 descends lower down upon the interspace between the third and fourth centrums. The 

 fifth neural arch, as in the Oxford specimen, extends a little way across the interspace 

 between the fourth and fifth centrums, but nearly resumes its ordinary place. The 

 second and third sacral vertebrae are not so regularly convex below in the transverse 

 direction, but their sides converge so as to give a slight indication of a broad obtuse 

 ridge. The diameter of the spinal canal in the first and last sacral vertebrae is one 

 inch. 



T. II gives a side view of one of the sacral vertebras, and a great proportion of the 

 next vertebra, of the natural size, from the specimen of a portion of the sacrum of the 

 Megalosaurus in the British Museum. The characteristic shape of the bodies of 

 these vertebrae is better shown in the view of their inferior surface, T. III. But, 

 in one of the vertebrae, « 3, the transversely rounded or convex surface begins to 

 be modified into an almost carinate form of that surface. A similar difference of 

 the inferior surface may be noticed in the third and fourth sacral vertebrae of the 

 Iguanodon.* 



The terminal articular surface of the last sacral vertebra, which articulates with 

 the first of the caudal series, is shown in fig. 2, T. III. 



* Palaeontographical Society, 1854, ' Wealden Dinosauria,' Tab. III. 



