THE CAMBRIDGE GREENSAND. 623 
extends the length of the centrum, and looks obliquely outward and 
upward. The length of the centrum in this region varies between 
13 inch and 1,5 inch, The articular ends widen at the upper 
margin from little more than 1 inch to 1,4, inch, and the depth is 
about 154, inch. The sides are slightly comenue from back to front, 
and their curve is prolonged upward, continuous with the neural 
arch, which is always distinguished by the deep groove already re- 
ferred to. The succeeding four belong to the lower dorsal region ; 
in them the centrum increases in size and depth, and its side be- 
comes rather more convex. It still retains the basal ridge, which 
becomes sharper, and sometimes disappears, being marked by a 
tubercle at each end. In the earliest of these four vertebre, the 
height from the base of the centrum to the platform of the neural 
arch is rather more than 23 inches, and the length of the centrum 
is 1? inch, while its depth from the neural canal j is about 1,4, inch. 
In the largest and, apparently, last or last but one of the four, the 
width of the centrum at the anterior articular face, as preserved, is 
1,8, inch, while the depth of the centrum is about the same. From 
the decreasing height of the neural arch this vertebra may be sup- 
posed to be near to the sacral region. It is 1,8,inch long in the dorsal 
measurement, and less ventrally. The height to the platform of the 
neural arch from the middle of the base is "23 inches. 
The transverse processes are about 3 inch thick, but are fractured. 
The neural spine and zygapophyses are also broken away, but the 
zygapophyses look inward as well as upward. ‘The ninth dorsal 
vertebra differs so much from those with which it is associated, and 
recalls so strongly the dorsal region of Acanthopholis, that I am in- 
clined to regard it as having become accidentally mixed with the 
other remains. It is in the same state of mineralization, but is 
much longer, had a perfectly rounded base, was most compressed 
below the neural arch, and had circular articular ends, with a 
central pit, so that I feel no doubt that it ought not to be included 
in the definition of Syngonosaurus. 
Sacrum.—The sacrum (fig. 6, p. 624) has lost the neural arches, and 
consists, as preserved, of two portions, each of which includes parts of 
two vertebra, so that there were certainly no fewer than four, and 
may have been more. ‘The last dorsal described corresponds in size 
and character with the first sacral of the larger fragment, which 
has a similar flat, subtriangular, articular end (fig. 6, a), which is 
1,4, inch broad at the upper part, as preserved. The sides are conyex 
from above downward, and meet in a sharp keel in the middle of the 
base. The suture between the first and second vertebra is entirely 
obliterated. The depth from the neural canal to the middle of the 
base is 14 inch ; ee the second vertebra it becomes reduced to 1} inch. 
The fraement i is 3,5, inches long, which I estimate to be within atenth 
of an inch of the length of two vertebrae. The base of the second ver- 
tebra is much more conyex than that of the first, and the median 
keel is all but obliterated. The width of the centrum in the middle 
is rather less than 13 inch in the first sacral vertebra, and somewhat 
more in the second. The state of preservation is such that there are 
2u 2 
