320 Annals of the South African Museum. 



fibulae are much shortened, and if there is any interval between them, 

 it is a small foramen or slit which is enclosed above and below by 

 the meeting of these bones. 



For comparison of this species with previously described species 

 from the same or approximately the same horizon the cervical 

 vertebrae are of the greatest importance, since the skull is quite 

 unknown in the other species and only a few odd limb bones have 

 hitherto been found. The cervical vertebrae are very similar to those 

 of some of the nearly contemporaneous forms, particularly in the 

 presence of a sharply defined and deep central depression in the 

 middle of the more gently concave articular surfaces of the centra, 

 but in all cases differences are apparent which forbid the inclusion of 

 this form in any of the species hitherto described. 



The forms which seem to resemble the present species most 

 nearly are Plesiosaurus degenhardti Koken, P. limnophilus Koken, 

 and P. valdensis Lydekker, sp. ; there is also a certain amount of 

 similarity to P. bernardi Owen and some other species. 



In Plesiosaurus degenhardti * of Koken the form of the centra of 

 the cervicals differs considerably, the height of their centra being 

 greater than either their width or length ; in the present species 

 the width is the greater, and at the same time in P. degenhardti the 

 edges of the articular surfaces are more rounded and thickened and 

 the zygapophyses are smaller. The difference in the proportions of 

 the centra is shown if we compare centra of approximately the 

 same size of the two species : thus, in the present species, if the 

 length of the centrum be taken as 100, the width will be about 156, 

 the height 138 ; while in P. degenhardti, the length being 100, the 

 width will be 127, the height 152. 



From Plesiosaurus limnophilus t of Koken the difference is also 

 well marked, the length of the centrum being about equal to the 

 width, while in P. capcnsis it is much less. In a vertebra from the 

 Wealden of Cuckfield, Sussex, ascribed by Lydekker \ to P. limno- 

 philus, but regarded by Koken as probably distinct, the length and 

 height of the centrum are about equal, but the width is greater. 

 Comparison with Plesiosaurus valdensis $ shows a much more 

 marked similarity ; in this case, the length of the centrum being 

 taken as 100, the width is 151, the height 129 proportions which 



* Koken, Palaeont. Abhandl., vol. in.. (1887), p. 414; see also vol. vii. (1896),. 

 p. 122, pi. iii. 



f Koken, op. cit., vol. iii. (1887), p. 417. 



J Lydekker, Catal. Foss. Eept. Brit. Mus., pt. ii. (1889), p. 224. 



Lydekker, torn, cit., p. 188. 



