THE CAMBRIDGE GREENSAND. 621 
All the parts which are most characteristic of the Dinosaurian 
genera, such as the bones of the extremities, the pelvic and pectoral 
arches, and the teeth, are unfortunately wanting. We are hence 
compelled to rely on the forms of the vertebral centrums in esti- 
mating the affinities of this genus; and there are very few genera in 
which associated sets of vertebree from the several regions of the 
body enable one to make a satisfactory comparison. 
No other Dinosaurian genus known to me has the tail-vertebree 
so hexagonal, compressed, and elongated as in EHucercosaurus. Per- 
haps the tail of Hylwosaurus is least dissimilar, and the compressed 
visceral side of the earlier dorsal centrums may probably be taken 
to indicate an affinity towards the Iguanodont family. 
Part Y. 
On the Skeleton of Syngonosaurus macrocercus, Seeley, a Dinosaur 
from the Cambridge Greensand, preserved in the Woodwardian 
Museum of the University of Cambridge (figs. 6-8, pp. 424-626), 
INTRODUCTION. 
Syngonosaurus is founded upon a series of nineteen vertebrae, 
which represent the neck, back, sacrum, and tail; and in some 
respects these vertebrae offer evidence of affiliation to several Dino- 
saurian types, especially to Hucercosaurus. The early dorsal ver- 
tebre, however, are remarkably compressed from side to side, not 
merely at the base, but throughout the body; and ossification has 
progressed so far that, notwithstanding the somewhat battered con- 
dition in which the remains are preserved, the neural arches are 
constantly united to the centrums. In the lower dorsal region the 
compressed condition of the centrum is only recognized in the great 
vertical depth of the bone. The ridge on the visceral surface 
gradually disappears, till it is represented by a mere tubercle below 
the anterior and posterior articular ends. The ridge, however, re- 
appears in the sacrum, where the depth of the centrum becomes 
greatly diminished, in the usual manner. The caudal vertebrae at 
first had centrums with the articular faces oblique, slightly pro- 
celous, and in close juxtaposition, indicating the tail to have 
been stiff. The chevron bones formed a single large facet, which 
appears to have obliquely truncated the lower half of the posterior 
face. The facet is represented by a sutural surface, probably indi- 
cating that these bones were large as well as firmly adherent. Ten 
vertebree are preserved from the back, four from the sacrum, and five 
from the earlier part of the tail. These tail-vertebre have the 
centrum much compressed from side to side below the transverse 
processes ; but the visceral surface, though narrow, is well rounded. 
The other associated bones are imperfect fragments of a meta- 
tarsus badly preserved; and in the absence of better evidence of 
their pertaining to this vertebral column, I do not feel that they 
can be satisfactory evidence of the extremities. There are eleven 
pieces of dermal armour, large elongated plates, some of which 
Q.J.G.8. No. 140. 20 
