THE CAMBRIDGE GREENSAND. 597 
Early Caudal Vertebra (fig. 2).—The early caudal vertebra might 
be about the third. It has the centrum rather short, with the 
articular surface subcircular in front, and larger and subquadrate 
behind. The neural arch is moderate, with the compressed spine 
directed upward and backward; and the prezygapophyses extend 
outward in a V-shape, anterior to the face of the centrum. The 
transverse anchylosed caudal ribs are compressed from above down- 
ward, and directed outward and a little downward. 
Fig. 2.— Early Caudal Vertebra of Acanthopholis horridus, one half 
nat. size. (From a specimen in the British Museum.) 
a. Anterior view. 6. Left lateral view. 
The centrum, as in the early caudals of Scelidosaurus, has an 
aspect of leaning obliquely forward, partly owing to the articular 
surface for the chevron bones causing the posterior articulation of 
the vertebra to extend below the anterior articular margin, and 
partly in consequence of a real obliquity, as indicated by the angles 
made by the articular faces with the neural canal. The margins of the 
articular faces are apparently worn a little or roughened by de- 
composition. ‘The antero-posterior measurement of the centrum is 
1,5 inch below the neural canal, 1,2, inch through the middle of 
the concave articular faces, and nearly 1,4 inch towards the inferior 
visceral margin, so as to suggest a convex curve for the inferior 
outline of the tail. 
The anterior articulation is somewhat markedly concave from 
above downward, has a thick rough rounded border, and is as nearly as 
possible circular, with a diameter of about 1,%,inch. The pos- 
terior articulation is subquadrate, but a little wider than deep, the 
width being about 2,2, inch. The depth from the neural canal to 
the facets for the chevron bones 1,5; inch, and to the base of the 
centrum rather over 2 inches. ‘he least depth of the centrum 
from the middle of the neural canal to the middle of the basal 
visceral surface is 1,8,inch. The chevron facets, though prominent, 
