OPHIDIA. 143 



Figs. ]8, 19, 20, 21, give views of two of the best-preserved vertebrse of the present 

 form, which I have attributed to a distinct species under the name of Palaophis porcatus. 



The fourth modification of the Palseophidian vertebrae from Bracklesham is the 

 most common, and is characterised by the coextcnsion of the base of the hypapophysis 

 with the under surface of the centrum, or by the whole of the middle of that under 

 surface forming a ridge : both ends of the ridge being produced, the posterior one the 

 most, and forming the normal hypapophysis. These vertebrae are usually of large 

 size ; I have examined upwards of thirty, ranging between the extremes given in 

 figs. 25 and 26, PI. 3 ; and it is from this series that I have selected the type vertebra of 

 the genus PalaojMs, PI. 1, figs. 5-8. 



The ridge between the anterior and posterior zygapophyes in these vertebras is 

 absent (PI. 2, fig. 5) or interrupted (PI. 3, figs. 27, 28). There is no well-defined space 

 above the zygosphcne anterior to the base of the neural spine. These vertebrae I 

 regard as typical of the species Palceophis TyphcBus : they are rather longer in 

 proportion to their breadth than those of the PalaopMs porcatus. 



To this category belongs the vertebra with the unusually well-preserved neural spine 

 (fig. 27), and likewise the two vertebrse which are preserved in their natural connexion, 

 showing the reciprocal interlocking of their complex articular processes (fig. 28). 



The fifth form of the vertebrae from Bracklesham is characterised by the com- 

 pression of the centrum and the convergence of its almost flattened sides to the ridge 

 on the inferior surface, from which a single hypapophysis is developed. I have examined 

 not more than four such vertebrae, including the two which are anchylosed together, 

 those (figs. 32-34, PI. 3) being the smallest in size, and the vertebra (figs. 29-31, 

 PI. 3) the largest. The ridge between the anterior and posterior zygapophyses is 

 suppressed ; the neural arch gently swells out as it descends from the base of the 

 neural spine, and from between the zygapophyses it bends in to coalesce with the 

 converging sides of the centrum. This vertebra has not that character of a caudal 

 vertebra, which is manifested in the Pytlion and most modern Oplddla by the transverse 

 pair of hypapophyses ; it shows plainly the base of a single median hypapophvsis from 

 near the posterior surface of the centrum (fig. 34). The diapophyses of fig. 29 are 

 broken away, together with the anterior concave end of the centrum ; had they been 

 entire, we might have derived from them evidence of the more constant character of 

 the caudal vertebrae of Serpents, which is derived from the coalescence of a short and 

 straight pleurapophysis with the diapophysis, lengthening out that transverse process, 

 as in fig. 42. The zygosphene and zygantra are developed, as, indeed, they continue 

 to be to near the end of the tail in modern Serpents ; and the produced angle of the 

 posterior border of the neurapophysis is as characteristic of the small compressed 

 vertebrae of the PalcBOjjhis (fig. 29) as of the larger specimens. 



The two anchylosed vertebrae belonging to the compressed series have been already 

 alluded to. The base of the neural spine is limited to the posterior half of the neural 

 arch in both (fig. 33). The hindmost of the two vertebrae is the longest, measuring 



