THE CAMBRIDGE GREENSAND. 603 
These centrums are exceedingly similar inform, butincreaseslightly 
in length as they pass down the back, and when placed together in 
sequence, with their articular faces in contact, form an upward arch, 
which is unlike the straight horizontal column of the Crocodile, and 
suggests, I think, that the body may have been carried in a semi- 
erect position, as was certainly the condition in so many of the Di- 
nosauria. The form of the centrum, which is well rounded on the 
underside (fig. 2a), is remarkably Teleosaurian. The position of 
each vertebra in the series is determined by length, size of the 
articular ends, and shape, width, and degree of excavation of the 
area which forms part of the neural canal, there being a marked 
increase in width and depth on nearing the sacrum, while the neural 
area widens posteriorly on nearing the neck. 
The first centrum of the series is fractured transversely, as though 
by a stroke of the workman’s pick, and only the posterior half is 
preserved. It shows the articular area for the neural arch to be ex- 
ceedingly broad, and the posterior face of the centrum is very slightly 
concave, being much less impressed in the middle than in the cer- 
vical region. The second dorsal measures 1,2; inch from front to 
back, has an aspect of slight compression from side to side, where it 
measures 1 inch in the middle of the centrum, becoming a little 
wider towards the neural arch. The depth of the centrum from the 
neural canal is 1,4, inch. The posterior articular face is almost 
absolutely flat. The third dorsal is rather better preserved ; it 
measures 1,3, inch in length, is rather more flattened at the sides 
and ends, and has the neuro-central suture so uniform that the back 
of the vertebra can only be recognized by the nutritive foramina in 
the neural canal being placed slightly behind the middle line. The 
fourth dorsal slightly increases in length, and is more compressed 
below the neuro-central suture, so that the articular faces of the 
centrum become vertically elongated, measuring, as preserved, 1,%, 
inch in depth and 1,3, inch wide. ‘The fifth to the twelfth centrums 
are about 14 inch long, and have the sides of the neural canal rather 
narrower than in the earlier dorsal region, the sides being sub- 
parallel, with a slight expansion at both the anterior and posterior 
ends. ‘The neuro-central suture is slightly convex from back to 
front, is marked with transverse grooves, as in Teleosaurs, and in 
the seventh centrum the lateral compression reduces the transverse 
measurement in the middle of the suture to $4 inch. Towards the 
end of the dorsal series the articular face of the centrum is more 
nearly circular, and it becomes flat at one end, and somewhat con- 
cave at the other. There is no certain evidence on the matter ; but 
I am inclined to regard the somewhat larger end with the concavity 
as anterior, on the ground that the neuro-central sutural surface is 
somewhat wider towards the concave end. Hence there would 
seem to be an approach towards a procelous articulation in the 
lower part of the back, which may be a functional development con- 
sequent upon a semierect mode of progression. ‘The last dorsal is 
much longer in the neural than in the visceral measurement, the 
extreme length being 14% inch, There is no important change in the 
