﻿KIMMERIDGE CLAY. 



55 



one side, as shown in PI. XVI, fig. 2. This distortion I conceive to be due to movements of 

 the matrix after the fossil had been inclosed thereby and become petrified therewith. For, 

 being thus supported at every point by the matrix, during the slow and continuous partial 

 pressure, the spine has yielded and bent without breaking. In one instance the sustaining 

 neural arch has suffered partial fracture at the side (ib., fig. 1), toward which the spine 

 has been bent. 



A thickening at the outer side of the neurapophysis, feebly indicated in the larger 

 anterior caudals (PI. XV, fig. 2, np) 3 becomes more prominent near the base of the prezy- 

 gapophysis, as at np, figs. ] and 2, PI. XVI, in the succeeding smaller vertebrae, in 

 which the hypapophyses are more distinctly marked. 



These articular protuberances (ib., figs. 1 — 3, hy) form a pair at the hind border of 

 the inferior surface of the centrum ; the articular tracts at the fore border of that surface 

 are barely defined, or may be indicated by an extension backward of the rough marginal 

 syndesmosal tract. 



The caudal vertebra in PI. XVI is figured a little more than half the natural size. The 

 answerable caudals in the great Monitor Lizard {Varanus niloticus) are given, of the 

 natural size, in figs. 4 and 5. 



The haemal arch in the caudal vertebra, with a centrum 5^ inches in vertical extent, 

 has the same length. The haemapophyses (ib., fig. 2, h) are 2| rd inches in length before 

 coalescing to form the spine (ib. ib., hs) } which is 2^rd inches in length in the subject of 

 the Plate ; it was probably longer when quite entire. But the length of the arch and 

 spine was plainly less in proportion to the vertical extent of the rest of the vertebra than in 

 Cetiosaurus longus. The hypapophyses are accordingly relatively smaller, and are limited 

 to a narrower transverse extent of the inferior surface of the centrum (ib., fig. 3, hy) than 

 in Cetiosaurus, or in the recent Varanus (PI. XVI, fig. 4, hy). In Cetiosaurus brevis 

 (Pal. vol. for 1857, T. X) the hypapophysial facets (h, h) are broader and Avider apart 

 than in Cetiosaurus longus. 



In Iguanodon the reverse conditions prevail. These surfaces have become confluent, 

 and present a single bilobcd facet to the similarly confluent surfaces on the bases of the 

 right and left hsernapophyses. Both neural and haemal spines are relatively longer in 

 Iguanodon ; and the neural spine springs from a smaller proportion of the hind part of 

 the neural arch at a much greater distance behind the prezygapophyses 1 than in 

 Omosaurus. The caudal vertebrae differ less from each other in Omosaurus and Cetio- 

 saurus than they do in either of these genera as compared with Iguanodon. 



As in the case of Cetiosaurus longus and other Dinosaurian subjects of previous Mono- 

 graphs, I have selected the best preserved specimen of an average-sized vertebra for the 

 subject of figures of the natural size. As the number of these monstrous dragons 

 increases, the judgment of the Council of the Palaeontographical Society in voting the cost 



1 Pal. Monogr. for 1854, tt. viii and ix. See also the young or small kind of Iguanodon, Mon. cit., 

 t. i, h, in which this vertebral character is significantly repeated. 



