SKULL OF A PARIASAURIAN REPTILE. 175 
vacuity, the thrusting back of the acetabulum till it lies entirely 
behind the sacrum and the size of the latter, make the whole very 
mammalian ; another feature in which this type resembles the 
Therapsids is the reduction of the phalangeal formula. 
It is therefore necessary to compare the skull of Pariasaurus 
with that of a Therapsid; before doing so it will be convenient to 
discuss what are really the essential features of that great group. 
The group Therapsida was founded by Broom to include all 
the South African reptiles which are admittedly closely related, 
i. e. the Anomodontia, “ Cynodontia,” ‘ Therocephalia,” Deino- 
cephalia, and Dromasauria. Jt will be most convenient to see 
what characters are really common to all these types, then to 
discuss which of these characters are common also to other great 
groups of early reptiles which are admittedly not very closely 
related, and which features may be regarded merely as a primitive 
inheritance, and so to discover by elimination what characters are 
really diagnostic of the group. I have been able to examine 
satisfactory material of all the orders, that of the Dromasauria, 
which I only know through the kindness of Dr. Broom, being the 
least satisfactory in details of cranial structure. 
The Deinocephalia are large reptiles of very massive structure. 
Skull with one temporal vacuity surrounded by the squamosal 
and postorbital (or by the same two bones with the parietal in 
addition ?). No temporal bone except the squamosal. Temporal 
region short and pineal foramen far back. The occiput composed 
of a plate with very small laterally placed posttemporal fosse, 
the supraoccipital overlapped by the vertically placed interparietal 
and tabulares, which are entirely on the back of the skull, and 
the latter of which reach down outside the posttemporal fosse to 
the ends of the opisthotics. Brain-cavity very high. [Opening 
to inner ear placed low down?] Stapes in contact with the 
quadrate. Quadrate large, partially overlapped behind by the 
squamosal ; a quadratojugal present. Palate not well known. 
Septomaxillary present on the face; lachrymal not reaching 
septomaxillary. 
Lower jaw with flat angular, with a notch on the lower border. 
No intercentra behind the atlas ; ribs double-headed throughout 
the presacral part of the column ; four sacral vertebree ¢ 
Two coracoidal elements, the anterior not contributing to the 
glenoid cavity. 
Pelvis with a short vertically placed ilum; pubis and ischia 
meting each other to form a plate-like pelvis. 
Humerus of an expanded and twisted type, with an entepi- 
condylar foramen. 
[This description is founded on the British Museum material of 
Tapinocephalus and closely allied genera. | 
