SKULL OF A PARIASAURIAN REPTILE. 7S 
(5) The retention of three temporal bones. 
(6) The primitive palate, identical in all important features 
with that of the primitive embolomerous Stegocephalia. 
(7) The primitive humerus with a huge entepicondyle. 
[(8) The single sacral rib. From the conditions found in 
carboniferous embolomerous Stegocephalia I am inclined to 
doubt if this is really primitive. | 
(9) The ordinary pelvis. 
(10) The expanded ribs. 
And in the following specialisations :— 
1i) The loss of the cleithrum. 
(12) The loss of the posterior coracoidal element. 
Diadectes and its allies differ considerably less from Paria- 
saurus than does Seymouria in most features, whilst they possess 
many advanced characters in which they differ from it more than 
does the latter type. 
The only primitive features in which Diadectes differs from 
Pariasaurus are : 
1. The retention of a supratemporal. 
2. The expanded ribs. 
3. The large entepicondyle of the humerus. 
4. The simple pelvis. 
Diadectes differs in the following advanced characters :— 
5. The posttemporal vacuities are closed. 
6. The postparietals and tabulares are placed more on the 
back of the skull than on the dorsal surface, so that they overlap 
the supraoccipital. 
7. The common development of hypopophysial articulations. 
The two types agree in many characters, for example :— 
1. The concave basioccipital condyle. 
2. The fact that the vertically placed quadrate is far forward. 
3. The fact that the anterior part of the brain-case is sur- 
rounded by bone, which in Pariasaurus is a single sphenethmoid 
whilst in Diadectes it is said to be a paired “alisphenoid,” but 
there is no doubt that the conditions are essentially similar. 
These characters are all primitive ones. 
There is in fact no doubt whatever that Diadectes and Paria- 
saurus are not in the least closely allied, but represent two lines 
differing fundamentally in the evolution of the brain-case, which 
in Pariasawrus is depressed and articulates with the roof of the 
skull only by a supraoccipital which is a solid narrow pillar 
separating large posttemporal vacuities and articulating with the 
lower surface of the parietal and postparietal ; whilst in Diadectes 
the brain-cavity is high and the supraoccipital is expanded into a 
wide plate which is overlapped by tl:e downturned postparietals. 
It is difficult to compare Pariasaurus with Limncscelis, for no 
