96 REPORT — 1841. 



most gigantic specimens of Saurian remains that enrich it. They include the 

 bodies of two dorsal vertebrae and four entire caudal vertebrae, which, if not 

 consecutive, seem to have come not from distant parts of the basal portion of 

 the tail of the same individual ; there are also the bodies of several of the 

 smaller posterior caudal vertebrae. 



No. ^ (" Gigantic vertebra of Igucmodon" MS. Catalogue of Mantellian 

 Collection,) is a posterior dorsal vertebra of the Cetiosaurus hrevis, and ex- 

 hibits in a striking manner the peculiar characters of this species, viz. the 

 great depth and breadth, especially the latter dimension, as compared with 

 the length or antero-posterior diameter of the centrum or body of the ver- 

 tebra. 



The posterior articular facet is, in this region of the spine, more concave 

 than the anterior surface, a structure which approximates to that peculiar one 

 which characterizes the Streptospondylus *. The contour of the articular 

 ends is a full transverse oval : the middle of the centrum is strongly con- 

 tracted, slightly concave in the longitudinal direction at the upper part of 

 the side of the centrum, but deeply concave below, and with a slight indica- 

 tion of a broad, obtuse longitudinal ridge along the middle of the concave 

 under surface. In the Iguanodon the sides of the vertebral body are nearly 

 flat in the vertical direction ; in the Cetiosaurus they are strongly convex. 

 The surface at the middle of the vertebra is longitudinally striated with very 

 fine, subparallel, short impressions : these grow deeper and more irregular at 

 the thick, rugged and everted margins of the ai'ticular ends. 



The neurapophyses are firmly anchylosed here, as in the caudal region, 

 and the line of the primitive suture is hardly discernible : their base is shorter 

 than the short centrum, and is attached nearer its anterior part : in the Igua- 

 nodon the neural arch is very nearly coextensive in antero-posterior diameter 

 with the centrum supporting it : in a dorsal vertebra, of an Iguanodon 4^ 

 inches in breadth, the antero-posterior extent of the base of the neural arch 

 is 4- inches : in the present vertebra, which exceeds 7 inches in breadth, the 

 antero-posterior extent of the base of the neural arch is 21 inches, and only 

 2 inches a little above the base. The outer side of the neurapophysis is con- 

 vex in the axis of the vertebra, and concave in the opposite direction as it 

 ascends to the base of the transverse process, without exhibiting a trace of the 

 ridges and hollows that so singularly characterize the same part in the dorsal 

 vertebrae of the Streptospondylus Cuvieri. The antero-posterior diameter of 

 the base of the transverse process is 2 inches ; its vertical diameter 1 inch. 

 The diameter of the spinal canal is 1 inch 9 lines. The articular surfaces of 

 the anterior oblique processes are flat, and look upwards and slightly inwards. 

 In the Iguanodon their under margins, in the dorsal vertebrae, converge at 

 nearly a right angle : in the present vertebra they incline to each other at an 

 angle of 40°. The spinous process begins to rise immediately behind the 

 anterior oblique processes by a narrow vertical plate, which seems as if it 



* Since the vertebrae of the Streptospondylus lose their peculiar convexo-concave charac- 

 ter by the gradual subsidence of the anterior ball, as they approach the tail, the cervical 

 vertebrae of the Cetiosaurus may approach, more nearly than do the dorsal ones, to the con- 

 vexo-concave structure of the Streptospondylian vertebrje. The fact that, hitherto, only 

 cervical vertebriE of the great Streptospondylus, and only dorsal and caudal vertebrae of the 

 Cetiosaurus, have been discovered in the Wealden formations, has induced me well to con- 

 sider the grounds for assigning them to Saurians of distinct genera. But the general con- 

 stancy of the vertebraj of the same Saurian in their antero-posterior diameter, forbids the 

 supposition of a vertebra of six inches in length in the neck being associated with one of 

 three inches in length in the back. Additional evidence of a very decisive character must 

 at least be obtained before the great Cetiosam- can be admitted to have resembled the Ptero- 

 dactyle in such disproportionate length of the cervical vertebrae. 



