236 J. W. HULKE ON POIKILOPLEURON BUCKLANDI. 
close resemblance of their centrum to that of the acknowledged 
trunk-vertebre of Megalosaurus Bucklandi, allowance being made 
for such modification, chiefly reduction of complexity, which in 
every vertebral column is observed in passing from trunk to tail; 
and, further, they are quite applicable to caudals of Megalosaurus 
preserved in public collections. 
With its characteristic tibia and astragalus not distinguishable 
from those of Megalosaurus Bucklandi, and with the extreme simi- 
larity of the form of the vertebrae, what grounds exist for retaining 
the genus Potkilopleuren ? 
The distinctness of Povkilopleuron has been affirmed by Prof. Owen, 
partly on the ground of the greater simplicity of its vertebrae as com- 
pared with those of Megalosawrus, but mainly on the presence of a 
medullary cavity in the body of the vertebra in Potkilopleuron, 
which he did not find present in a caudal of Megalosawrus. As 
regards the former of these reasons, the caudals of Deslongchamps’s 
Porkilopleuron have indubitably a simpler figure than that of the 
trunk-vertebre of Megalosaurus, but not than that of its caudal 
vertebree ; and as regards the second reason, unless the caudal 
ascribed to Meqalosaurus, in which no medullary cavity was found, 
was discovered in such association with other undoubted Megalo- 
saurlan remains as to positively identify it with this Dinosaur (and 
this is not mentioned), I would suggest that the determination must 
be held to be one of probability only, since in the caudals of Croco- 
diles and of the carnivorous Dinosaurs a strong common likeness 
exists. Possibly the question is one which cannot be decided by the 
section of a single vertebral centrum of uncertified origin from a 
part of the vertebral column where generic characters are less 
sharply expressed. That there should be a medullary cayity in 
genuine Megalosaurian caudal vertebree would not be improbable, 
since in the neural arch in trunk-yertebre, and in the sacrum, 
medullary cavities were noticed by the late Prof. Philips in type 
specimens in the Oxford University Museum*. I have myself seen, 
in the collection of G. B. Holmes, Esq., a fine vertebral centrum 
which had the characters commonly assigned to trunk-vertebre of 
Megalosaurus, and in which, when broken across, Mr. Holmes 
found a large hollow space occupying nearly half the length of the 
centrum. It may be objected that this was actually a vertebra of 
Poikiloplewron and not of Megalosaurus. Conceding such a mistaken 
determination, it shows how extremely alike are their vertebrae 
when they cannot be distinguished by their figure. 
The evidence adduced in favour of the generic distinctness of 
Poikilopleuron is, 1 venture to submit, so weak contrasted with that 
in fayour of its identity with Megalosaurus Bucklandi, that I con- 
fidently expect Deslongchamps’s generic name will be discontinued, 
and Poikilopleuron Bucklandi be known in future as Megalosaurus 
Buckland. Had Deslongchamps himself possessed the more abun- 
dant material for a comparison of the Megalosaurian skeleton with 
the remains of his Saurian which are now available, and had the 
* Geol. of Oxford and Thames Valley, by Prof, J. Phillips, p. 206, figs. 2, 3. 
