458 BRITISH FOSSIL REPTILES. 



surface is smooth at the middle part, with longitudinal, irregularly wavy ridges 

 and grooves for an inch at the margin, which are well defined ; this roughness 

 indicates the attachment of the fil)res of the capsular ligament. The fore-and-aft 

 diameter of the centrum is less at the summit than at the base ; here it measures 4 

 inches 6 lines; along the neural canal it is 4 inches; the smooth tract caused by 

 the impress of this canal is 6 lines across the narrowest part, and 2 inches across 

 the widest end. The neurapophysial pits are shallow, with a rugged surface 3 

 inches 6 lines long by 1 inch 9 lines in diameter; the small part of the upper 

 surface of the centrum not covered by the neurapophysis is at the end where the 

 neural canal is widest, and which is most probably the hinder end ; there are two 

 venous foramina on one side and three on the other side of the middle of the lower 

 surface of the centrum. The breadth of the articular surface is 6 inches 3 lines ; 

 its depth, or vertical extent, the same. 



The same conformity, in regard to their proportional size, characterises the 

 teeth of Poly]>tychodon and the associated large Plesiosauroid vertebrae from 

 Kursk. I am indebted to the able engineer and zealous palaeontologist, Colonel 

 KiprianofiF, for the opportunity of examining the specimens discovered by him in 

 that locality. 



The centrum of one of these vertebae belonging to the dorsal region, from the 

 Neocomian formations at Kursk, measures 4 inches in length and 5 inches 4 lines 

 in breadth ; the terminal articular surfaces are flat ; between them the lower surface 

 of the centrum is strai':;ht, but at the sides it is gently concave; there are two 

 venous foramina, 2 lines apart, at the middle of the under surface of the centrum. 



Portions of ribs from the Upper Green-sand of Cambridgeshire agree in 

 texture, and correspond in proportional size, with the cervical and dorsal vertebral 

 bodies with which they were associated. I have selected one of these fragments 

 for representation in PI. 31, fig. 3, because it shows a well-marked ridge («) on 

 one side, a character I have not seen in the ribs of true Plesiosauri ; and these portions 

 of ribs, of probably FoJypfychodon, present a less rounded transverse section. 



Atlas and Axis {Enaliosauria, PI. 32). 



The centrums of the first and second cervical vertebrae coalesced, as in Plesio- 

 saunis, from the same locality and formation as the hinder cervical vertebra, p. 457, 

 PI. 31, present the proportions, in regard to their antero-posterior diameter, of the 

 cervical vertebras of Pliosaurus ; but they belong, in all probability, to the same 

 Plesiosauroid reptile as the vertebrae previously described, and I refer them to the 

 genus Polyptychodon. 



Like most of the fossils from the Haslingfield locality, they had been subject to 

 attrition. The contour of the centrum of the atlas {Eiialiosauria, PI. 32, fig. 1) has 

 been subcircular; its anterior articular surface (e, a,) is concave, and has afl'orded 



