THE CAMBRIDGE GREENSAND. 599 
hexagonal and moderately concave. The depth of the anterior 
face is rather less than an inch; the width from side to side in the 
Fig, 3.— Middle Caudal Vertebra of Acanthopholis horridus, nat. size. 
(In the Museum of Practical Geology.) 
a. Right lateral view. 6. From beneath, showing median longitudinal groove. 
middle of the centrum is 1,4, inch. The upper outline of the 
neural arch is straight and oblique. The depth from the posterior 
end of the neural arch to the base of the centrum is 1,%, inch, while 
in front the corresponding measurement is 1,4,inch; the width over 
the anterior zygapophyses is4} inch. The posterior end of the neural 
arch (which is imperfectly preserved) tapers. The lengthof the union 
between the neural arch and centrum is ;8,inch. The ridges on the 
sides of the centrum are only developed towards the articular ends. 
This vertebral column is quite distinct from that of any other 
genus, though, as indicated by Prof. Huxley, it closely approaches 
to Scelidosaurus. There is a close general correspondence in the 
form of the dorsal centrum, though in the lower part of the back 
Scelidosaurus appears to haye the body of the vertebra more com- 
pressed from side to side. The early caudal vertebrae in Scelido- 
saurus are longer, and more oblique, and have the neural spine less 
inclined backward. The later caudal vertebree in Scelidosaurus are 
much more elongated than in Acanthopholis, have the body more 
constricted, and have no trace of the inferior median groove or of the 
lateral ridges of Acanthopholis, while the form of the neural arch is 
altogether different, The basal groove, form of the caudal centrum, 
