290 DE. C. W. ANDREWS 0:ff A NEW PLESIOSAUR [vol. Ixxviii, 



of hard substance Avhich under the microscope seems to show some 

 resemblance to calcified cartilage. There does not seem to be an}'- 

 question of epiphyses on the ends of each centrum, but merely of a 

 simple intervertebral disc (PL XIV, tig. 5, i.v.d.). Possibly the 

 large size and prominence of the zygapophyses, the convexity 

 of the outer rim of the articular surface of the centra, and the 

 presence of this disc may be connected with increased flexibility 

 in some directions of this region of the column. In the dorsal 

 region the thickened rounded border of the articular surface is 

 wanting, and the concavity begins at the edge which is sharply 

 defined, also the zygapophyses are smaller and less prominent : 

 here the successive centra must have been in direct contact, and 

 the degree of flexibility consequently much less. The neural 

 spines of the cervical region are rather short, and curve backwards ; 

 the convexity of their anterior border is greater than the concavity 

 of the posterior, so that they narrow towards their apex, which is 

 occupied by a deep pit, probably marking the position of a carti- 

 laginous extension in life. Towards the dorsal region the neural 

 spines {n.sp.) lengthen somewhat, become more upright, and are of 

 nearly the same width throughout their length. 



The cervical and thoracic vertebrae are specially valuable for com- 

 parison with those of other Plesiosaurs, since in very many cases the 

 skull and other characteristic portions of the skeleton are unknown. 

 The most notable character of these vertebrae in the species now 

 described is the form of their articular surfaces. A similar type of 

 vertebra occurs in Plesiosaurus capensis Andrews, P. degenliarclti 

 Koken, P. hej^nardi Owen, Gimoliosaurus valdensis Lydekker, and 

 in Brancasaurus hrancai Wegner ; also to some degree in Plesio- 

 saurus arcuatus Owen. Flesiosaurus degenliardti is, however, 

 distinguished from this species by the possession of cervical centra 

 which are higher than wide, neural spines with their anterior and 

 posterior borders parallel, and relatively small zygapophyses. 

 In P. degenliardti^ if the length of the centrum be taken as 

 100, the width is 127, the height 152 ; in the specimen here 

 described, if the length be taken as 100, the width is 155, the 

 height 146. 



Comparison with the cervical of the type-specimen of Cimo- 

 liosaurus valdensis Lydekker^ shows that the form now described 

 resembled that species in the shape of its neural spine, but differed 

 in several other respects. Thus, in C. valdensis the zygapophyses 

 are relatively smaller and less prominent, and their articular faces 

 are more nearly horizontal. The articular ends of the centrum are 

 more nearly circular, and their central concavity (though dee^)) 

 has not the sharply-defined central depression. In Cimoliosaurtcs 

 hernardi the articular ends of the cervicals are deeply concave 

 with a convex outer border, but here also the sharply-defined 

 central depression is wanting ; in this species, too, there is a 

 strongly-marked oblique ridge running up the side of the arch from 



1 Cat. Foss. Rept. Brit. Mus. pt. ii (1889) p. 188, fig-. 61. 



