THE CAMBRIDGE GREENSAND. 615 
have a rounder lateral outline, and in having the visceral keel, 
which is about 54, inch wide in the middle, defined by a groove on 
each side. What I take to be the posterior articular face of the 
centrum is decidedly concave. Both of these specimens appear to 
have suffered from rubbing in the mill at the washing from which 
they were obtained. Several vertebrae are missing between the 
second and the third of the series preserved. The third centrum is 
1,4 inch long dorsally, and rather less at the visceral margin, 
showing that the back was probably arched convexly. The sides of 
the centrum are much more inflated, and the visceral keel has disap- 
peared from the middle of the base of the centrum, though it is 
still indicated by strong rugosities at the two ends. The side of 
the centrum adjacent to the articular ends continues this rugose 
condition round the side by means of short wavy ridges. The 
visceral surface was somewhat rubbed before fossilization ; but the 
articular ends, as preserved, are nearly circular. The anterior face 
is 1,9, inch deep, slightly cupped, with a central boss. The poste- 
rior face is 1,8, inch wide, moderately cupped, but without any 
central elevation. The articular margins are a little worn, but 
appear to have been rounded. Again, several vertebrae are missing 
between the third and fourth. All trace of the visceral keel has 
now disappeared, and the centrum has again become slightly 
deeper than wide, and has a somewhat compressed aspect at the 
sides, owing to itsdepth. The rugose marks for ligamentous attach- 
ment are relatively stronger and longer than in the earlier vertebre. 
There is a small nutritive foramen more than a third down the side 
and intermediate between the two ends. Similar foramina occur in 
the previously described vertebrae. This centrum is 1,8, inch long 
on the neural surface, and apparently less on the visceral surface, 
though one end of the specimen had decomposed from maceration 
before it was fossilized. The articular ends are slightly concave, and 
the posterior end is nearly 2 inches deep and 14% inch wide, as pre- 
served. ‘The lines of the neuro-central suture are nearly obliterated 
by decomposition, but the least width of the centrum in the middle 
is 1,5 inch. 
Sacrum.—Of the sacrum three vertebre are preserved. They so 
far closely correspond with sacral vertebre of Anoplosawrus as 
strongly to suggest that in this genus also there were at least six 
elements in the sacrum. ‘The two bones, which have the forms of 
second and third vertebree (fig. 4, a, 6, p. 616), fit together by natural 
surfaces, and show that the sacral elements were in the closest possible 
bony union, short of anchylosis, the coadapted intercentral sur- 
faces being irregular. There is, however, some difficulty in adapting 
the third sacral vertebra to the articular surface of the fourth (?) (¢) ; 
so that it would seem more probable that another vertebra should 
have been introduced between them. But the anterior end of the 
fourth (?) centrum was destroyed by decomposition before fossiliza- 
tion, and the posterior surface is partly destroyed by fracturage 
since it was exhumed. And when the three centrums are placed 
together in sequence resting on the visceral surfaces as they pro- 
