OPHIDIA. 145 



Twelve vertebrae of progressively increasing size repeat the characters of the 

 vertebrae (fig. 6) ; i. e. they have the fore part of the under surface between the 

 diapophyses excavated, and have only one inferior spine, viz. the hypapophysis 

 developed from the hind part of the under surface ; they have also the zygosphenal 

 articulations nearly vertical, and raised high above those of the zygapophyses (fig. 8). 

 A vertebra (figs. 22, 23, 24) of the same size as the largest of these twelve differs from 

 them, and repeats the general characters of the small vertebra (fig. 14) : it has the 

 anterior as well as the posterior hypapophysis ; larger terminal cup-and-ball surfaces in 

 proportion to its size ; smaller intervals between the zygosphenal and zygapophysial 

 articulations (fig. 24) ; less lofty posterior aliform extensions of the neural arch, and the 

 base of the neural spine extending nearly to the fore part of that arch. These vertebrae, 

 and especially the larger specimens (figs. 18, 20) have a sti'ong external ridge extending 

 from the anterior to the posterior zygapophyses on each side of the neural ai'ch. On 

 comparing one of these vertebra with another of the ordinary character and of the 

 same size, the following further differences presented themselves : in the ridged vertebrae, 

 wliich are provisionally referred for the convenience of description and comparison to a 

 distinct species, with the name of Palceophis porcatus, the articular ball is broader in 

 proportion to its height (compare fig. 23 with fig. 27) ; the anterior zygapophyses are 

 more produced outwards and less produced forwards, so that they do not extend 

 beyond the border of the articular cup, so far as in the non-ridged vertebrae of 

 Palceophis TyplicBus ; the fore part of the zygosphene in the ridged vertebrae is broader, 

 and less excavated. The breadth of the base of the neurapophysis is greater in the 

 ridged vertebrae than in the unridged ones, in proportion to its length. The articular 

 surfaces of the zygapophyses are smaller in the ridged than in the unridged vertebrae. 



Figs. 13, 18, 20, 22, PL 3, show the ridged character of the sides of the neural 

 arch in Palceophis porcatus, and fig. 19 shows the consequent superior breadth of the 

 base of that arch in relation to the length of the vertebra as compared with fig. 8, 

 PI. 2, a corresponding vertebra of the PaJaophis Ti/phaus. Fig. 14 in the same Plate 

 shows the striking difference in the proportions of the same part of the vertebra in the 

 Pytlion tiyris. 



Such are the observed differences which seemed worthy of mention in tlie series of 

 Palaeophidian vertebrae from the Eocene deposits at Brackleshara which I have had 

 the opportunity of comparing. The nature of the differences may be interpreted in 

 different ways : with regard to the small vertebrae, for example, those with a single 

 spine from the posterior part of the under surface (figs. 1, 2, 3, PL 3) may be small 

 cervical vertebrae of the same species as that to which the large vertebrae with the two 

 inferior spines belong; and the small vertebrae with two inferior spines (figs. 14, 15) 

 may have belonged to a smaller and younger individual of the same species, and have 

 come from a more posterior part of the vertebral column of such individual. The 

 anterior vertebrae of both Pythons and Boas, for example, are distinguished by an 



