310 TEETIAEY VEETEBEATA OF THE EATtTM. 



a ridge runs downwards and forwards to the base of the anterior zj-gapophyses (see 

 PI. XXVI. fig. 4 b). These processes, which may perhaps be described as enormously 

 developed anapophyses, are present, though of very small size, in some of the vertebrae 

 of PaloeopMs. The genus was founded by Lucas for the reception of the species 

 P. schuclierti, a large snake from the Eocene of Alabama, where it occurs associated 

 with remains of Zeuglodons. In the Eocene of Egypt, also, there is one species, 

 likewise associated with the remains of Zeuqlodon. 



Pterosphenus schweinfurthi (Andrews). 



[Plate XXVI. figs. 4-6.] 

 1901. Maeriophis scliwewfurthi, C. W. Andrews, Gqol. Mag. [4] vol. vili. p. 438, fig. 2. 



Tjipe Specimev. — A dorsal vertebra (PL XXVI. fig. 4) ; Geological Museum, Cairo. 



This species is distinguished from P. schucherti by having the posterior face of the 

 neural arch above the zygantrum considerably more expanded, so that the free portions 

 of the postei o-lateral processes are shorter. 



Form. & Loc. — Qasr-el-Sagha beds (Middle Eocene) : north of Birket-el-Qurun. 



The vertebrae of this species occur in great numbers scattered along the Middle 

 Eocene escarpment, but only in very rare cases are even two found united or so 

 situated that they may be reasonably supposed to belong to the same animal. 



The procoelous centrum is considerably elongated, and is about as wide as it is 

 high; the anterior cup is deep and nearly circular in outline, except beneath the 

 neural canal, where its border is straight; the posterior convexity is nearly hemi- 

 spherical. On the ventral surface there is a strong median hypapophysial ridge {hyp.), 

 usually produced into two forwardly and downwardly directed processes, one situated 

 close to the anterior end of the centrum, the other near the middle. The transverse 

 processes {t.p.) are short and situated ventro-laterally on the anterior end of the 

 centrum, below which they project considerably ; their outer ends bear the vertically 

 elongated convex surfaces for the ribs, looking downwards and outwards. From the 

 position of the rib-facets it appears that the body must have been laterally compressed 

 to a considerable degree. From the upper ends of the transverse processes a ridge 

 runs upwards and forwards to the anterior angles of the prezygapophyses {a.z.), 

 which project considerably in front of the centrum ; their oval articular facets are a 

 little below the level of the floor of the neural canal, and look upwards and a little 

 backwards. The articular surfaces of the zygosphene {zs.) are almost parallel with 

 those of the prezygapophyses ; they are borne on the ventral face of two prominent 

 processes, the upper edges of which unite to form the anterior border of the neural 

 spine. The postzygapophyses {p.z.) look downwards and a little forwards, their 

 surfaces being about on a level with the top of the centrum. The zygantrum [za.) 



