J. W. HULKE ON THE VERTEBE-^ OP OENITHOPSIS. 33 



to 2 centim. above the floor of the neural canal, and above this 

 again rapidly increase. The arch and processes exhibit the singu- 

 larly complex structure, less perfectly shown in my first fossil, shown 

 here in 1870. The inner aspect of each praezygapophysis has an 

 additional articular surface which, prolonged into the bottom of the 

 deep notch that separates the pair of praezygapophyses, forms with 

 this a zygantral arrangement. In correspondence with this a ver- 

 tical zygosphenal bolt-plate depends from the confluent inner ends 

 of the postzygapophyses. Prom the bottom of this zygosphenal 

 plate two sheets of bone descend upon the neurapophyses, roofing in, 

 after the fashion of an eave, the posterior opening of the neural 

 canal. The prae- and postzygapophyses are connected by a x^latform 

 continued along the neural arch in the level of its crown. This 

 platform is produced outwards and upwards in the form of a strong 

 and rather long transverse process, the free end of which is stout 

 and clubbed as for the attachment of a rib-tubercle. Below, a thin 

 vertical plate descends from the transverse process and platform 

 upon the side of the neural arch, on which it is lost slightly below 

 the mid height of the latter. Above, a similar thin plate connects 

 the platform with the neural spine. The articular surface for the 

 rib-head is just outside the praezygapophysis. Under the platform 

 are very deep cavern-like recesses. The neural spine arises by two 

 pairs of plates, of which the front are thinner, and spring from the 

 crown of the very lofty arch close to the praezygapophyses. Below, 

 these anterior plates are separated by a deep mesial groove. Above, 

 they gradually approach, the separating groove lessens till they meet, 

 when they again diverge and lose themselves in the anterior as- 

 pect of the transversely extended free end of the spinous process. 

 The posterior pair, stouter, more pillar-like, arise directly over 

 the postzygapophyses. They are not traceable so high as the ante- 

 rior pair. Below, between them, immediately above the zygosphe- 

 nal plate, is a deep pit. Above this they are separated by a narrow 

 median crest which ascends nearly to the top of the spinous pro- 

 cess, and served for the attachment of an interspinous ligament. 

 The transverse expansion of the free end of the spinous process, 

 so that the direction of its greatest measurement here crosses the 

 axis of the vertebral column, audits deep sculpturing, are two re- 

 markable features. 



Until now our ideas of the form of these singular vertebrae had 

 been drawn constructively from fragments of detached arches and 

 centra. The association of arch and centrum, which in 1870 

 I felt justified in affirming, on the evidence of such fragments, 

 is hero first actually demonstrated in this magnificent fossil. 

 Another centrum, apparently from the same part of the vertebral 

 column as that just described, is 24 centim. long. The articular 

 ball is 22 centim. in its vertical diameter, and 16 centim. in 

 the horizontal. The under surface of the centrum is somewhat 

 flattened. The chambers and their lateral openings are very large. 

 A third centrum, about 23 centim. long, has a more cylindroid 



Q. J. G. S. No. 141. D 



