toy L. Moodie 447 
I have examined. To be sure there are in the young of the turtles pads 
of cartilage which form the articular surfaces such as are found on the 
limb bones of the Amphibia, but in the turtles there is no distinct separa- 
tion of the cartilage from the diaphysis as in some of the Amphibia, nor 
is there any trace of any bony structure. The shaft is entirely ossified 
from its center of ossification and the cartilaginous pad becomes in time 
fully osseous by such a process. The pad of articular cartilage often 
makes a distinct line on the bone which becomes evident when the carti- 
lage is macerated. I have noticed such lines on the limb bones of the alli- 
Fic. 2. Longitudinal section of a propodial of a Sauropterygian; from the 
Kimmeridge Clay of Ely. a@=—Endochondral bone (Proximal epiphysis). 
b=Endochondral bone (Distal epiphysis). c@—Perichondral bone (Shaft). 
d= Medullary cavity. ™4 natural size. After Lydekker. (lLydekker’s inter- 
pretations in parentheses.) 
_ gator and various turtles. Doubtless the line to which Parsons refers is 
due to the articular cartilage on the great trochanter. 
In the Plesiosauria there have long been known some propodial bones 
of young animals which offer very puzzling characters. One of these 
specimens (Fig. 2) is in the British Museum and was figured diagram- 
matically by Lydekker in his Catalogue of fossil Reptiles and Amphibia 
(7). Parsons has also given a diagram of a young propodial, whether of 
the same bone or not I do not know. Another well known specimen is the 
