South African Fossil Beptiles. 475 
if a small opening exists between the parietal, the squamosal, and the 
post-temporal, the Pelycosaurs might nevertheless be pretty nearly related 
to the Therocephalians. 
Taking into consideration the structure of the skull and other parts of 
the skeleton, the conclusion to which I come is that the Pelycosaurs and 
the Therocephalians are groups sprung from a common and not very 
remote ancestor. The Pelycosaurs retain a number of the more primitive 
characters, but are in many respects highly specialised. The Thero- 
cephalians are more generalised, but considerably more highly evolved. 
The Pelycosaurs were slow-moving crawlers with short, lizard-like limbs ; 
the Therocephalians were active runners with mammal-like limbs. The 
difference in the structure of the limb girdles is in harmony with the 
differences in the limbs. 
When we look at other American Permian types we again find curious 
resemblances to African forms. The order Gotylosauria includes a number 
of types which agree in having the temporal region roofed, but some of 
those placed in the order are manifestly not very nearly related to the 
others. Diadectes, which is the type of the order, is fortunately well 
known. It is a large, heavily built animal, with short, feeble limbs. The 
vertebrae are very like those of the South African Pareiasaurus, and 
though superficially there are striking differences in most other parts of 
the skeleton, fundamentally there is a surprising similarity. As the 
Therocephalians differ from the Pelycosaurs in having walking limbs, so 
Pareiasaurus differs from Diadectes in having large powerful limbs which 
could easily keep the body off the ground, and the girdles are modified to 
suit the new habit. Unfortunately the structure of the skull of Pareia- 
saurus is not well known, but the agreement is sufficient to justify us in 
concluding that Pareiasaurus is related to Diadectes in much the same 
way that the Therocephalians are to the Pelycosaurs. 
Another small type that is at present placed in the Gotylosauria is 
called Pariotichus, or, as Dr. Case informs me, it ought to be called 
Captorhinus. This is a small lizard-like Cotylosaur which was of fairly 
active habit, and has evolved to a considerable degree along the line 
which gave rise to the Ehynchocephalians. It differs from Diadectes 
and Pareiasaurus in having a rounded instead of a flat occipital condyle, 
and with the exception that the temporal region is roofed and the pre- 
coracoid is still retained, there is little, if anything, to distinguish it from 
the primitive Ehynchocephalians. To us at present its chief interest lies 
in the fact that it is distinctly related to the South African forms Sauro- 
sternon and Procolophon. The African types are more specialised, but 
they are probably more nearly related to GaptorJiinus (Pariotichus) than 
are the Therocephalians to the Pelycosaurs. 
In the American Permian beds are many Stegocephalians, of which 
