448 



J. W. nULKE ON IGTJANODON PaBSTWICRII 



Measurements. 





Last 

 Lumbar. 



1st 

 Sacral. 



2nd 

 Sacral. 



3rd 

 Sacral. 



4th 

 Sacral. 



5th 

 Sacral. 



Wealden Sacrum. 



(No. 37685, Brit.- 



Mus. Oat.) 



Length along under- 



surface 



Transverse horizontal 



diameter at middle 



of centrum 



mm. 

 71 



(N0.Z3) 

 52 



69-5 



mm. 

 62 



35 



(No. 24) 

 56'^ 



44 



mm. 

 80 



28 



(No. 25) 

 52* 



41-5 



mm. 

 65 



28 



(No. 26) 



52* 



43 



mm. 

 76-5 



28* 



(No. 27) 



52* 



43 



mm. 

 76 



65 



Cumnor Iguanodon. 



Length of centrum... 



Horizontal transverse 



diameter at middle 



of centrum 





That these differences of form have a specific value will be, I 

 think, allowed by all. The fewer sacral vertebrae in the Cumnor 

 sacrum have a somewhat higher import. Have we here an earlier 

 phase in the development of the Dinosaurian sacrum than that 

 exemplified in /. Mantelli ? The earlier age of the Cumnor Igua- 

 nodon, as indicated by its gisement, Kimmeridge Clay, would be in 

 harmony with this. 



Tail. — Thirty-five postsacral vertebrae are recovered. It is 

 probable that a couple of the foremost are missing, since all those 

 procured have chevron-facets, and in extant lizards and crocodiles 

 these are absent from a small number of the foremost caudal 

 vertebras. 



In No. 28, probably the foi-emost of our series, the centrum is 

 larger than in those which I have placed behind it. The anterior 

 articular surface is nearly plane, very slightly concave, whilst the 

 posterior surface, as in all the other caudal vertebrae, is distinctly 

 concave. The sides of the centrum are, in the vertical direction, 

 gently convex ; they meet at the under surface of the centrum in a 

 blunt wedge-form. In the longitudinal direction they are gently 

 concave. The under surface at each end is encroached on by the 

 chevron-facet, which is continuous with the terminal articular 

 surface. In this vertebra (No. 28) the length of the neural surface 

 is 50-5 millims., and the distance between the anterior and pos- 

 terior chevron-facet on the under surface is 19 millims. A strong 

 transverse process juts out from the neur apophysis at the height of 

 12 millims. above the neuro-central suture. 



No. 29 (PL XIX. fig. 9) has a peculiar and distinctive obliquity, 

 produced by the downward and backward slant of its under surface, 



* Approximate measurements ; small chips off edge prevent actual measure- 

 ments of this dimension. 



