10 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [ Nov. 10, 
laps and is firmly united with the pubis, and a posterior process 
_ which becomes very thick behind and articulated with the post- 
acetabular process of theilium. The shaft of the bone is flattened 
laterally, and has a thick and rounded posterior edge. Anteriorly 
it is thinner, and at 2°75 inch from the acetabulum it is produced 
into a broad and long decurrent process, the free edge of which 
overlaps the pubis. Such a process is very generally developed in 
birds. Beyond this process the ischium widens out, and seems to 
terminate in a spatulate free end, like that of the corresponding part 
of the ischium in Megalosaurus and Iguanodon. ‘This spatulate ex- 
tremity is broken away from the right ischium, but remains on the 
other side (/s’). And their relative position leads to the belief that the 
two bones united in a ventral symphysis. The long diameters of 
the ischia and pubes are parallel, and they are directed downwards 
and backwards in such a manner as to make an obtuse angle with 
the anterior half of the long diameter of the itum. Hypsilophodon is 
the first reptile in which this disposition of the ischium and pubis 
has been observed. 
Eleven caudal vertebre in series, with a rudiment of a twelfth at 
the posterior end, and another which lies on one side of these, all 
belonging to the anterior part of the tail, are represented in the 
plate cited, but they have been worked out much further since it 
was published. The characters of some of the vertebre are very 
well shown. For example, the third from the anterior end in the 
series of eleven now exposed, is 2 inches high from the lower edge 
of the centrum to the summit of the spine (Pl. I. figs.6&7). The 
centrum is 0:8 inch long, while its articular faces are 0°6 inch high. 
The transverse measurements of the articular faces of the centrum 
cannot be ascertained in this vertebra ; but that of the posterior face 
of the vertebra which lies by itself is 0°5, the length of the ver- 
tebra being 0-7 inch. ‘The spine of the ‘‘ third” vertebra measures, 
from the postzygapophysis to its truncated extremity, 0°85 inch, and 
0-36 inch from before backwards ; the spines of all the caudal ver- 
tebree are slightly inclined backwards. The root of a transverse 
process (or caudal rib), 0-36 inch long, stands out at right angles 
from the upper part of the side of the centrum, its posterior edge 
inclining forwards. The under face of the centrum is concave from 
before backwards, and presents a narrow and flattened surface, 
traversed by a longitudinal groove. The zygapophyses are long, 
and the planes of their articular faces are almost vertical. The 
obliquely truncated surfaces for the articulation of the chevron 
bones at the anterior and posterior ends of the ventral face of each 
centrum are well marked. No chevron bone is attached to the 
vertebra under consideration ; but several lie, one on the top of the 
other, beneath the fifth to the eighth vertebra of the caudal series. 
The best-preserved of these is 1-75 inch long, 0-38 inch wide at the 
vertebral end (Pl. I. fig. 8). The vertebral ends of the forks of the 
chevron bones are expanded and ankylosed together in the manner 
characteristic of the Dinosauria. 
The length of the left femur is 5:7 inches, or rather less than the 
