SKULL OF A PARIASAURIAN REPTILE. 167 
of the optic nerves, but the olfactory nerves pass out in front, 
of it. 
A bone exactly corresponding to this in all its relations occurs 
in many Stegocephalia ; it has been figured as a‘ Rhinencephalic 
chamber” by Williston in Cacops and Aspidosaurus novomexicanus, 
the latter specimen giving evidence from the fact that it is dis- 
placed, that it is not a downgrowth of the bones of the skull 
roof, By Fraas it has been figured but not determined or de- 
seribed in COyclotosaurus posthumus, and it also occurs in some 
specimens of “‘ Lothriceps” hualeyi.* 
It is, however, much best shown in a skull in the Pretoria 
Museum found at Senekal, O. F.8., which is one of the speci- 
mens described by v. Hoepen as Myriodon senekalensis. In that 
specimen the roofing bones have been split away leaving the 
impression of their lower surface on the matrix, through an 
extremely thin and transparent film of which the upper surface 
of the sphenethmoid is clearly seen to be quite continuous over 
the brain. None of these specimens shows the distinction of the 
bone from the parasphenoid of which it might conceivably be an 
outgrowth ; but a large and well-preserved skull apparently of a 
form very near to Capitosaurus, which I found on the farm 
Watford, Dist. Albert, Cape Colony, in the Cynognathus beds, 
shows the bone clearly, and it is extremely spongy, quite different 
from the hard membrane-bone of the parasphenoid. 
No. 36358 in the British Museum is a fragment of a skull of 
Capitosaurus nasutus, Meyer, from Bernberg. It shows the right 
side of the face with the orbit, and on the back of the specimen 
part of the vertical plate of pterygoid which passes backward 
to the quadrate. In advance of this lies the sphenethmoid, only 
the right wall of which’ is preserved, and that with its inner 
surface destroyed so that the loose cancellar tissue is visible. 
The posterior end of the bone has a notch which présumably 
transmitted the optic nerve, and the anterior end is also notched. 
This bone is extremely clearly shown to rest in the deeply grooved 
upper surface of the parasphenoid. 
This specimen affords conclusive evidence that the ‘ rhinen- 
cephalic chamber” is a separate bone, for there can be no 
doubt of the interpretation of the present fragment, as the bone 
from its structure is obviously not the prootic, and also lies far 
in advance of the actual position of that bone in all known 
Stegocephalia. It is therefore certain that a bone surrounding the 
anterior part of the brain and separating the exits of the olfactory 
and optie nerves, which lies freely between the parasphenoid and 
the membrane-bones of the roof of the skull, occurs in many 
Temnospondylous and Stereospondylous Stegocephalia, and as it 
agrees exactly in all features with the sphenethmoid of the frog 
should be called by that name. 
The bone which has been described above as surrounding the 
* Since this was written Broom has described the sphenethmoid in Hyvyops. 
