THE IGUANODON AND HYL^EOSAURUS. 
297 
articulaires 'posUrieures petites, pointnes, rapproch^es, et donnant dans deux petites 
fossettes entre les anterieures et aii-devant de labasse de I’epineuse,’ ‘Elies doivent 
appartenir a une espece de Sauriens tres-voisine des Plesiosaurus.’ Ocular inspec- 
tion can alone safely indicate the propriety of associating these vertebrae together as 
belonging to the same species or genus. Probably the mutilated remains of a large 
Saurian, from the lower greensand at Hythe, may belong to this genus, and also the 
teeth of the provisional ^ Polyptychodon occurring in the same formation. The 
Wealden deposits intercalated between two marine formations, contemporaneous with 
them in a certain sense, may well contain a few vertebrae of the great Saurians whicii 
swarmed along the shores of the bays indenting the “ Country of the Iguanodon,” 
or even entered occasionally the mouths of its mighty rivers. If these four caudal 
vertebrae are specifically different from any found in the more ancient oolite, to pre- 
vent confusion, and to remove the objection that may well be raised against the 
nomen trivi ale ‘brevis' — for who will venture to indicate the relative length of an 
animal with no known affine, from four of its anterior caudal vertebrae ? — we propose 
to name the species to which they belong, Cetiosaurus Conyheari, in honour of the 
Dean of Llandaff, one of the earliest, ablest, and most distinguished geologists and 
palaeontologists of England. 
The massive sacrum of the Iguanodon (Plate XXVI.) is composed of a series of six 
vertebrae anchylosed together in a nearly straight line; the neural arches unite at an 
early period above the intervertebral foramina, and form a tunnel over the spinal 
canal, while the short spinous processes coalesce into a thick median ridge. The 
bodies of the second, third, and fourth vertebrae, are only half as broad as those of the 
first and two last, which are of nearly equal width, but all have the same length. 
The free articular surface («') of the first sacral is flat or rather slightly convex, 
especially in the vertical diameter, and presents an oval contour ; the posterioii facet 
of the sixth (a") is subcircular and slightly concave, but deepest above. 
The body of each is more or less constricted in the centre, so that their surfaces 
are deeply concave lengthwise ; this contraction, and the marked expansion towards 
the articular facets, is most striking in the smaller middle vertebrae, least so in the 
first; and the more or less rounded transverse ridges at the lines of anchylosis give 
the inferior surface of this chain an undulating outline. The neural lamina of the 
first sacral about its root is much contracted in the antero-posterior diameter, and 
chiefly from behind forwards, so as to leave a large tract of the body exposed poste- 
riorly, while the anterior notch is comparatively shallow. The neural laminae of the 
four succeeding vertebrae are displaced slightly forwards, so that the anterior extre- 
mities of their bases rest upon and excavate the postero-superior angles of the bodv 
in front, and are also, perhaps, partly wedged into the intervertebral space ; each how-, 
ever impresses and is mainly attached to its own centrum ; and that of the last sacral 
is restored almost to its normal position, projecting only slightly beyond the anterior 
aspect of the body, leaving a portion of its upper surface uncovered behind, to form 
