740 MR. D. M. S. WATSON ON 
prezygapophysis of the axis. The atlas is very short from back 
to front. The proatlas is paired (and articulates with the skull ?). 
The remaining presacral vertebre are all much alike, but their 
neural arches become heavier as they are traced backward. The 
centra are completely pierced by the notochord and are consider- 
ably constricted, the lower surfaces, however, being flattened. 
The articular ends are expanded. There are intercentra between 
all the presacrals ; these are single crescentic bones of an ordinary 
character. Broom records paired intercentra between the third 
and fourth vertebree. I have not seen this region. 
The neural arches are heavy, extremely so in the posterior 
part of the column. The articulating faces of the zygapophyses 
are flat and placed horizontally throughout. The neural spines 
are only represented by very short projections on the top of the 
swollen neural arch. 
The rib articulations are single, carried at the end of a short 
transverse process, contributed to by both arch and centrum, in 
the anterior part of the column; with the progressive increase 1n 
size of the neural arch this process becomes obsolete, but the rib 
articulation remains essentially similar. 
The first sacral vertebra is very short anteroposteriorly ; it 
carries a very large rib articulating with both arch and centrum, 
and its neural arch is heavy. The anterior zygapophyses are 
wide apart, but the posterior facets are placed close together. 
The second and third sacral vertebre have slender arches, but 
their articulation-faces are still flat and horizontal. The caudal 
vertebre are not well exposed in any specimen ; anteriorly they 
resemble the posterior sacrals, but further back they develop 
fairly high spines and long chevron bones. It is not known how 
far back they carry ribs. 
The ribs are single-headed throughout and present no feature 
of interest. There is some evidence of a rib on the atlas, and 
there are certainly ribs on all the other presacral vertebra except, 
perhaps, the last two or three, on which I have not seen any; 
even in a well-preserved skeleton, if present, they were short. 
Abdominal ribs.—Three specimens show the whole series of 
abdominal ribs. The plastron is extremely reduced, consisting of 
at most five series of transverse rows each composed of six very 
small slender elements. These are divided into two groups, which 
do not meet in the middle line. The whole arrangement is about 
a centimetre from back to front, and lies about 15 mm. behind 
the pectoral girdle, cf. text-fig. 4, B. 
Pectoral girdle—The general features of the pectoral girdle 
have long been known. 
The scapula stands nearly vertically and is a simple bone with- 
out an acromion. It has a ridge down its outer surface and 
thickens considerably at the glenoid cavity. The anterior part of 
the lower margin of the bone is in contact with the precoracoid, 
and for the anterior half of this union the external surface of 
one bone is directly continued on to the other. Posteriorly this 
