OPHIDIA. 59 



in the Crotalus ; for the ball of the centrum, the posterior zygapophyses, and the 

 zygantral articulations, are present on the back part of the second of these anchylosed 

 vertebrae. But before further pursuing the description of this remarkable specimen, I 

 shall premise a brief notice of the vertebrse which have presented other modifications. 



In the series of Palaeophidian vertebras from Bracklesham, which I have had the 

 opportunity of comparing, a few, as has been already remarked, appear to have 

 come from the fore part of the body by the length of the hypapophysis, as compared 

 with the size of the vertebrae, which is small ; a character that adds to the likelihood 

 of their having come from that extremity of the series. Fig. 1, T. XIV, shows one of 

 these vertebrae in which the hypapophysis {h) is entire ; it is shorter and much more 

 compressed than that process is in the anterior trunk-vertebrae of the Python, fig. 4, 

 and its base extends forwards, as a sharp ridge, to between the diapophyses (fig. 3), 

 where like them, it has been mutilated by fracture. The zygapophyses are small, and 

 there is no ridge continued from the anterior to the posterior one ; the neurapophysis 

 presents the characteristic angular production (fig. 1, n), and the neural spine (ib., m) 

 is coextensive with the supporting arch. 



The second form of vertebra is characterised by a single and moderately-developed 

 hypapophysis, the base of which is confined to the hinder half of the under surface of 

 the centrum, leaving the fore part of that surface concave where it expands between 

 the bases of the diapophyses. I have received twelve such vertebrae from Bracklesham, 

 varying in size between the two extremes given in figs. 5, 6, and 10, 1 1, 12, T. XIV. The 

 hypapophysis {h) which is best preserved in the vertebra fig. 10, is shorter but thicker 

 than in fig. 1 ; the articular cup and ball are relatively smaller ; the zygosphene (zs) 

 is larger, and its surfaces larger and more vertical (fig. 5) ; the neural spine has a less 

 antero-posterior extent. These may be vertebrae from the hinder part of the abdomen, 

 near the beginning of the tail. Some of them have a minute ridge at the middle of 

 the anterior inferior concavity (fig. 9). 



A third modification of vertebra shows the same limited extent of the base of the 

 posterior hypapophysis, but a second shorter hypapophysis is constantly developed 

 from the middle of the space between the bases of the diapophyses. I have examined 

 twenty of such vertebrae ranging in size between the extremes given in figs. 14, 15, 

 and 17, T. XIV. As compared with fig. 5, the articular cup of fig. 14 is larger, the 

 zygosphene less, and of a different shape, concave anteriorly and not straight above, but 

 forming an obtuse angle there. A ridge is continued from the posterior to the anterior 

 zygapophysis (fig. 13). 



This ridge is more strongly developed in the larger vertebrae with the same 

 modification of the under surface (figs. 20, 21). The articular ball of the diapophysis 

 would seem not to have descended so low down as in the typical vertebrae referred to 

 Pal. Typhous. The neural spine does not extend to the fore part of the zygosphene ; 

 there is a short but well-defined space above zygosphene in front of the spine. 



