THE CAMBRIDGE GREENSAND, ~~ 617 
The vertebra which from its resemblance to the fourth sacral of 
Anoplosaurus (fig. 4, c) | regard as holding that place in the series 
measures rather more than 1,7, inch in length, and has a broad shallow 
channel on the median part of the visceral surface, deeper, however, 
than in Anoplosaurus. This is bounded laterally by two broad well- 
rounded ridges, into which it merges, and which terminate inferiorly 
the comparatively flat sides of the centrum. At what I take to be 
the anterior end these ridges are a little more divergent than at the 
posterior end. The base of the centrum has no sharply defined 
border, but is about 5%, inch wide at the articular ends. What 
remains of the sides of the centrum is only sufficient to show that 
these were moderately concave from front to back, and compara- 
tively flat and divergent from below upward. Only a small frag- 
ment of the neural canal is preserved, enough to show that the 
depth from this surface to the base of the centrum towards the 
middle of the vertebra was about 1; inch. The sides appear to 
haye diverged outward anteriorly, as though to give attachment to 
small sacral ribs; but behind the indication of this anterior infla- 
tion, of which there is no trace in Anoplosaurus, there appears to 
haye been a broad rounded prolongation of the side upward towards 
the neural canal, as though for the passage of an intervertebral 
nerve. There is nothing to indicate the deep excavation of the 
centrum for the expansion of the spinal cord in the sacral region ; 
but only evidence that the vertebral nerve, when given off, was 
prolonged downward instead of upward. The small fragment of 
neural surface is flat. 
The centrum which corresponds best in form with the second 
sacral of Anoplosaurus (fig. 4, 2) has become naturally fractured and 
enlarged before fossilization, as a consequence of maceration and 
absorption of phosphatic material. It is broad and deep, expanded 
at the posterior end, but with the base and sides so well rounded 
as to form about two thirds of a circle. The anterior end, which 
is roughened from decomposition and the natural rugoseness of the 
articular face, is vertically semiovate, being, as preserved, 2,4, inches 
wide below the neural canal, and 1,4, inch deep. The posterior end 
widens as though to give attachment to strong sacral ribs, and 
measures from side to side nearly 2,4, inches, while as preserved 
it is only 14 inch deep; hence the crumpled irregular articular face 
is transversely subreniform. ‘The indications of the neural surface 
are comparatively flat, widening posteriorly, and widest just in 
front of the sacral ribs, where it may be presumed that sacral nerves 
were given off. 
Of the third sacral element (fig. 4, 6) nothing remains but the 
basal portion of the centrum. It is 14% inch long, 1,4, inch wide 
posteriorly at the sides, which are flat and vertical, and rounded 
into the nearly flat base, which is slightly concave from front to 
back and slightly convex from side to side. Ona level with the 
base, at the anterior ends of the sides, are large facets fully an inch 
long for sacral ribs. ‘The articular ends appear to haye the same 
rugged faces noticed in the preceding sacral element. 
